| Message ID | 1398374579-5697-3-git-send-email-przanoni@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: > From: Paulo Zanoni <paulo.r.zanoni@intel.com> > > We still have way too many bugs with DP link training. We keep > switching between "narrow and fast" and "wide and slow", we recently > added 5GHz support, and whenever there's a bug report, we have to ask > people to apply patches and test them. > > Wouldn't it be so much better if we could just ask them to boot with > some specific Kernel boot option instead of applying a patch? This > will move the situation from "i915.ko is completely broken!" to > "i915.ko's default values are broken, but there's an option I can set > to fix it, so I won't need to learn how to compile a Kernel!". > > Some useful values: > - i915.dp_link_train_policy=1 for "wide and slow" > - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, > which should be able to fit 1920x1080@60Hz and 24bpp > - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on > not-so-huge modes > > The default behavior is still the same. > > Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> Yeah, I like this. I'll sign up Todd to review this all. > --- > drivers/gpu/drm/i915/i915_drv.h | 1 + > drivers/gpu/drm/i915/i915_params.c | 8 ++++++++ > drivers/gpu/drm/i915/intel_dp.c | 39 ++++++++++++++++++++++++++++++++++---- > 3 files changed, 44 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h > index 7d6acb4..d5ae8dc 100644 > --- a/drivers/gpu/drm/i915/i915_drv.h > +++ b/drivers/gpu/drm/i915/i915_drv.h > @@ -1941,6 +1941,7 @@ struct i915_params { > bool reset; > bool disable_display; > bool disable_vtd_wa; > + int dp_link_train_policy; Small nit: bitfield-y stuff should be unsinged. > }; > extern struct i915_params i915 __read_mostly; > > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c > index d05a2af..8c358e7 100644 > --- a/drivers/gpu/drm/i915/i915_params.c > +++ b/drivers/gpu/drm/i915/i915_params.c > @@ -48,6 +48,7 @@ struct i915_params i915 __read_mostly = { > .disable_display = 0, > .enable_cmd_parser = 1, > .disable_vtd_wa = 0, > + .dp_link_train_policy = 0, > }; > > module_param_named(modeset, i915.modeset, int, 0400); > @@ -156,3 +157,10 @@ MODULE_PARM_DESC(disable_vtd_wa, "Disable all VT-d workarounds (default: false)" > module_param_named(enable_cmd_parser, i915.enable_cmd_parser, int, 0600); > MODULE_PARM_DESC(enable_cmd_parser, > "Enable command parsing (1=enabled [default], 0=disabled)"); > + > +module_param_named(dp_link_train_policy, i915.dp_link_train_policy, int, 0600); > +MODULE_PARM_DESC(dp_link_train_policy, > + "Choose strategy for DP link training " > + "(0=narrow and fast [default], 1=wide and slow. For other values, " > + "bits 11:8 are for the BW and bits 7:4 are for the nubmer of lanes, " > + "check intel_dp_compute_link_config() for more details.)"); > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c > index 884166b..25f7e1c 100644 > --- a/drivers/gpu/drm/i915/intel_dp.c > +++ b/drivers/gpu/drm/i915/intel_dp.c > @@ -800,11 +800,42 @@ static bool intel_dp_compute_link_config(int mode_clock, int bpp, > > mode_rate = intel_dp_link_required(mode_clock, bpp); > > - for (lanes = min_lanes; lanes <= max_lanes; lanes <<= 1) > + switch (i915.dp_link_train_policy) { > + case 0: /* Narrow and fast. */ > + for (lanes = min_lanes; lanes <= max_lanes; lanes <<= 1) > + for (bw_it = min_bw_index; bw_it <= max_bw_index; > + bw_it++) > + if (link_config_is_possible(mode_rate, lanes, > + bws[bw_it])) > + goto found; > + case 1: /* Wide and slow. */ > for (bw_it = min_bw_index; bw_it <= max_bw_index; bw_it++) > - if (link_config_is_possible(mode_rate, lanes, > - bws[bw_it])) > - goto found; > + for (lanes = min_lanes; lanes <= max_lanes; lanes <<= 1) > + if (link_config_is_possible(mode_rate, lanes, > + bws[bw_it])) > + goto found; > + default: /* Bits 11:8 contain the index of the bws array. > + * Bits 7:4 contain the number of lanes. > + * Example: i915.dp_link_train_policy=0x140 uses > + * DP_LINK_BW_2_7 and 4 lanes. */ > + bw_it = (i915.dp_link_train_policy >> 8) & 0xF; > + lanes = (i915.dp_link_train_policy >> 4) & 0xF; > + > + if (bw_it < min_bw_index || bw_it > max_bw_index) { > + DRM_ERROR("Invalid BW index\n"); > + return false; > + } > + > + if (lanes < min_lanes || lanes > max_lanes || > + /* Not a power of two. */ > + !(lanes != 0 && (lanes & (lanes - 1)) == 0)) { > + DRM_ERROR("Invalid number of lanes.\n"); > + return false; > + } > + > + if (link_config_is_possible(mode_rate, lanes, bws[bw_it])) > + goto found; > + } > > return false; > > -- > 1.9.0 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
On Fri, Apr 25, 2014 at 10:06 AM, Daniel Vetter <daniel@ffwll.ch> wrote: > On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: >> From: Paulo Zanoni <paulo.r.zanoni@intel.com> >> >> We still have way too many bugs with DP link training. We keep >> switching between "narrow and fast" and "wide and slow", we recently >> added 5GHz support, and whenever there's a bug report, we have to ask >> people to apply patches and test them. >> >> Wouldn't it be so much better if we could just ask them to boot with >> some specific Kernel boot option instead of applying a patch? This >> will move the situation from "i915.ko is completely broken!" to >> "i915.ko's default values are broken, but there's an option I can set >> to fix it, so I won't need to learn how to compile a Kernel!". >> >> Some useful values: >> - i915.dp_link_train_policy=1 for "wide and slow" >> - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, >> which should be able to fit 1920x1080@60Hz and 24bpp >> - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on >> not-so-huge modes >> >> The default behavior is still the same. >> >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> > > Yeah, I like this. I'll sign up Todd to review this all. Now with Todd actually cc'ed. -Daniel
On Fri, 25 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote: > On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: >> From: Paulo Zanoni <paulo.r.zanoni@intel.com> >> >> We still have way too many bugs with DP link training. We keep >> switching between "narrow and fast" and "wide and slow", we recently >> added 5GHz support, and whenever there's a bug report, we have to ask >> people to apply patches and test them. >> >> Wouldn't it be so much better if we could just ask them to boot with >> some specific Kernel boot option instead of applying a patch? This >> will move the situation from "i915.ko is completely broken!" to >> "i915.ko's default values are broken, but there's an option I can set >> to fix it, so I won't need to learn how to compile a Kernel!". >> >> Some useful values: >> - i915.dp_link_train_policy=1 for "wide and slow" >> - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, >> which should be able to fit 1920x1080@60Hz and 24bpp >> - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on >> not-so-huge modes >> >> The default behavior is still the same. >> >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> > > Yeah, I like this. I'll sign up Todd to review this all. I guess we'll go with this then, but I'll step back from this particular patch for a bit, and share my concerns over module parameters and quirks. I am generally opposed to adding module parameters or quirks to workaround issues in features that should just work. They are an easy way out for things we should root cause and fix properly. Do not mistake me for an idealist for thinking this way, as I'm being pragmatic. The people who report bugs to us are roughly the same people who are capable of setting the module parameter. Once they figure that out, they'll stop responding to our requests for testing and info. We've seen this happen before. We'd hurt our chances of making things work out of the box for the average user. The more we add module parameters, the combinations of them explode. Debugging *other* problems becomes harder. In the bugs I work on, the #1 request I have is full dmesg, partially because I want to see all the wild kernel parameters the user might have set. And all too often they have. When there are module parameters that fix some bugs, the blogs and forums get filled with tips about them, and people use them, whether they strictly have the same bug or not. Search for i915 invert brightness for example. It's also not easy to drop module parameters after we've added them. You know the drill. Even after we've fixed everything the module parameter was supposed to fix, dropping it leads to https://xkcd.com/1172/. BR, Jani.
On Fri, Apr 25, 2014 at 12:00:34PM +0300, Jani Nikula wrote: > On Fri, 25 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote: > > On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: > >> From: Paulo Zanoni <paulo.r.zanoni@intel.com> > >> > >> We still have way too many bugs with DP link training. We keep > >> switching between "narrow and fast" and "wide and slow", we recently > >> added 5GHz support, and whenever there's a bug report, we have to ask > >> people to apply patches and test them. > >> > >> Wouldn't it be so much better if we could just ask them to boot with > >> some specific Kernel boot option instead of applying a patch? This > >> will move the situation from "i915.ko is completely broken!" to > >> "i915.ko's default values are broken, but there's an option I can set > >> to fix it, so I won't need to learn how to compile a Kernel!". > >> > >> Some useful values: > >> - i915.dp_link_train_policy=1 for "wide and slow" > >> - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, > >> which should be able to fit 1920x1080@60Hz and 24bpp > >> - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on > >> not-so-huge modes > >> > >> The default behavior is still the same. > >> > >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> > > > > Yeah, I like this. I'll sign up Todd to review this all. > > I guess we'll go with this then, but I'll step back from this particular > patch for a bit, and share my concerns over module parameters and > quirks. > > I am generally opposed to adding module parameters or quirks to > workaround issues in features that should just work. They are an easy > way out for things we should root cause and fix properly. > > Do not mistake me for an idealist for thinking this way, as I'm being > pragmatic. > > The people who report bugs to us are roughly the same people who are > capable of setting the module parameter. Once they figure that out, > they'll stop responding to our requests for testing and info. We've seen > this happen before. We'd hurt our chances of making things work out of > the box for the average user. > > The more we add module parameters, the combinations of them > explode. Debugging *other* problems becomes harder. In the bugs I work > on, the #1 request I have is full dmesg, partially because I want to see > all the wild kernel parameters the user might have set. And all too > often they have. When there are module parameters that fix some bugs, > the blogs and forums get filled with tips about them, and people use > them, whether they strictly have the same bug or not. Search for i915 > invert brightness for example. > > It's also not easy to drop module parameters after we've added them. You > know the drill. Even after we've fixed everything the module parameter > was supposed to fix, dropping it leads to https://xkcd.com/1172/. I fully agree with you. I'm working on a patch (only RFC thus far) which allows you to designate some module parameters as debug knobs. As soon as users touch them they'll get - a stern warning in dmesg - TAINT_USER'ed kernel That should be about as good as we can make it. -Daniel
On Fri, 25 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote: > On Fri, Apr 25, 2014 at 12:00:34PM +0300, Jani Nikula wrote: >> On Fri, 25 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote: >> > On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: >> >> From: Paulo Zanoni <paulo.r.zanoni@intel.com> >> >> >> >> We still have way too many bugs with DP link training. We keep >> >> switching between "narrow and fast" and "wide and slow", we recently >> >> added 5GHz support, and whenever there's a bug report, we have to ask >> >> people to apply patches and test them. >> >> >> >> Wouldn't it be so much better if we could just ask them to boot with >> >> some specific Kernel boot option instead of applying a patch? This >> >> will move the situation from "i915.ko is completely broken!" to >> >> "i915.ko's default values are broken, but there's an option I can set >> >> to fix it, so I won't need to learn how to compile a Kernel!". >> >> >> >> Some useful values: >> >> - i915.dp_link_train_policy=1 for "wide and slow" >> >> - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, >> >> which should be able to fit 1920x1080@60Hz and 24bpp >> >> - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on >> >> not-so-huge modes >> >> >> >> The default behavior is still the same. >> >> >> >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> >> > >> > Yeah, I like this. I'll sign up Todd to review this all. >> >> I guess we'll go with this then, but I'll step back from this particular >> patch for a bit, and share my concerns over module parameters and >> quirks. >> >> I am generally opposed to adding module parameters or quirks to >> workaround issues in features that should just work. They are an easy >> way out for things we should root cause and fix properly. >> >> Do not mistake me for an idealist for thinking this way, as I'm being >> pragmatic. >> >> The people who report bugs to us are roughly the same people who are >> capable of setting the module parameter. Once they figure that out, >> they'll stop responding to our requests for testing and info. We've seen >> this happen before. We'd hurt our chances of making things work out of >> the box for the average user. >> >> The more we add module parameters, the combinations of them >> explode. Debugging *other* problems becomes harder. In the bugs I work >> on, the #1 request I have is full dmesg, partially because I want to see >> all the wild kernel parameters the user might have set. And all too >> often they have. When there are module parameters that fix some bugs, >> the blogs and forums get filled with tips about them, and people use >> them, whether they strictly have the same bug or not. Search for i915 >> invert brightness for example. >> >> It's also not easy to drop module parameters after we've added them. You >> know the drill. Even after we've fixed everything the module parameter >> was supposed to fix, dropping it leads to https://xkcd.com/1172/. > > I fully agree with you. I'm working on a patch (only RFC thus far) which > allows you to designate some module parameters as debug knobs. As soon as > users touch them they'll get > - a stern warning in dmesg > - TAINT_USER'ed kernel Ah yes, I remember the patch, that's the one thing I was going to ask about before my colleagues insisted on leaving for lunch... What's the status and can we get that in first? BR, Jani. > > That should be about as good as we can make it. > -Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch
<snip> > Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> > --- > drivers/gpu/drm/i915/i915_drv.h | 1 + > drivers/gpu/drm/i915/i915_params.c | 8 ++++++++ > drivers/gpu/drm/i915/intel_dp.c | 39 > ++++++++++++++++++++++++++++++++++---- > 3 files changed, 44 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_drv.h > b/drivers/gpu/drm/i915/i915_drv.h index 7d6acb4..d5ae8dc 100644 > --- a/drivers/gpu/drm/i915/i915_drv.h > +++ b/drivers/gpu/drm/i915/i915_drv.h > @@ -1941,6 +1941,7 @@ struct i915_params { > bool reset; > bool disable_display; > bool disable_vtd_wa; > + int dp_link_train_policy; > }; > extern struct i915_params i915 __read_mostly; > > diff --git a/drivers/gpu/drm/i915/i915_params.c > b/drivers/gpu/drm/i915/i915_params.c > index d05a2af..8c358e7 100644 > --- a/drivers/gpu/drm/i915/i915_params.c > +++ b/drivers/gpu/drm/i915/i915_params.c > @@ -48,6 +48,7 @@ struct i915_params i915 __read_mostly = { > .disable_display = 0, > .enable_cmd_parser = 1, > .disable_vtd_wa = 0, > + .dp_link_train_policy = 0, > }; > > module_param_named(modeset, i915.modeset, int, 0400); @@ -156,3 > +157,10 @@ MODULE_PARM_DESC(disable_vtd_wa, "Disable all VT-d > workarounds (default: false)" > module_param_named(enable_cmd_parser, i915.enable_cmd_parser, int, > 0600); MODULE_PARM_DESC(enable_cmd_parser, > "Enable command parsing (1=enabled [default], > 0=disabled)"); > + > +module_param_named(dp_link_train_policy, i915.dp_link_train_policy, > +int, 0600); MODULE_PARM_DESC(dp_link_train_policy, > + "Choose strategy for DP link training " > + "(0=narrow and fast [default], 1=wide and slow. For other values, " > + "bits 11:8 are for the BW and bits 7:4 are for the nubmer of lanes, " > + "check intel_dp_compute_link_config() for more details.)"); There is a typo here, nubmer should be number, otherwise: Reviewed-by: Rafael Barbalho <rafael.barbalho@intel.com>
> -----Original Message----- > From: Intel-gfx [mailto:intel-gfx-bounces@lists.freedesktop.org] On Behalf > Of Daniel Vetter > Sent: Friday, April 25, 2014 10:19 AM > To: Jani Nikula > Cc: intel-gfx@lists.freedesktop.org; Zanoni, Paulo R > Subject: Re: [Intel-gfx] [PATCH 3/3] drm/i915: add i915.dp_link_train_policy > option > > On Fri, Apr 25, 2014 at 12:00:34PM +0300, Jani Nikula wrote: > > On Fri, 25 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote: > > > On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: > > >> From: Paulo Zanoni <paulo.r.zanoni@intel.com> > > >> > > >> We still have way too many bugs with DP link training. We keep > > >> switching between "narrow and fast" and "wide and slow", we > > >> recently added 5GHz support, and whenever there's a bug report, we > > >> have to ask people to apply patches and test them. > > >> > > >> Wouldn't it be so much better if we could just ask them to boot > > >> with some specific Kernel boot option instead of applying a patch? > > >> This will move the situation from "i915.ko is completely broken!" > > >> to "i915.ko's default values are broken, but there's an option I > > >> can set to fix it, so I won't need to learn how to compile a Kernel!". > > >> > > >> Some useful values: > > >> - i915.dp_link_train_policy=1 for "wide and slow" > > >> - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, > > >> which should be able to fit 1920x1080@60Hz and 24bpp > > >> - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on > > >> not-so-huge modes > > >> > > >> The default behavior is still the same. > > >> > > >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> > > > > > > Yeah, I like this. I'll sign up Todd to review this all. > > > > I guess we'll go with this then, but I'll step back from this > > particular patch for a bit, and share my concerns over module > > parameters and quirks. > > > > I am generally opposed to adding module parameters or quirks to > > workaround issues in features that should just work. They are an easy > > way out for things we should root cause and fix properly. > > > > Do not mistake me for an idealist for thinking this way, as I'm being > > pragmatic. > > > > The people who report bugs to us are roughly the same people who are > > capable of setting the module parameter. Once they figure that out, > > they'll stop responding to our requests for testing and info. We've > > seen this happen before. We'd hurt our chances of making things work > > out of the box for the average user. > > > > The more we add module parameters, the combinations of them explode. > > Debugging *other* problems becomes harder. In the bugs I work on, the > > #1 request I have is full dmesg, partially because I want to see all > > the wild kernel parameters the user might have set. And all too often > > they have. When there are module parameters that fix some bugs, the > > blogs and forums get filled with tips about them, and people use them, > > whether they strictly have the same bug or not. Search for i915 invert > > brightness for example. > > > > It's also not easy to drop module parameters after we've added them. > > You know the drill. Even after we've fixed everything the module > > parameter was supposed to fix, dropping it leads to > https://xkcd.com/1172/. > > I fully agree with you. I'm working on a patch (only RFC thus far) which allows > you to designate some module parameters as debug knobs. As soon as users > touch them they'll get > - a stern warning in dmesg > - TAINT_USER'ed kernel > > That should be about as good as we can make it. > -Daniel How hard would it be to expand the series afterwards this review to automatically try both "wide & slow" and "narrow & fast" for a given mode before giving up and logging the error? I can foresee us replying a lot to people saying try wide or narrow when we could have the driver do that for us. The link training policy then could just be used to debug things later for those special cases. I think this would be a good thing. For the whole series: Reviewed-by: Rafael Barbalho <rafael.barbalho@intel.com> > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
2014-04-25 6:00 GMT-03:00 Jani Nikula <jani.nikula@linux.intel.com>: > On Fri, 25 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote: >> On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: >>> From: Paulo Zanoni <paulo.r.zanoni@intel.com> >>> >>> We still have way too many bugs with DP link training. We keep >>> switching between "narrow and fast" and "wide and slow", we recently >>> added 5GHz support, and whenever there's a bug report, we have to ask >>> people to apply patches and test them. >>> >>> Wouldn't it be so much better if we could just ask them to boot with >>> some specific Kernel boot option instead of applying a patch? This >>> will move the situation from "i915.ko is completely broken!" to >>> "i915.ko's default values are broken, but there's an option I can set >>> to fix it, so I won't need to learn how to compile a Kernel!". >>> >>> Some useful values: >>> - i915.dp_link_train_policy=1 for "wide and slow" >>> - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, >>> which should be able to fit 1920x1080@60Hz and 24bpp >>> - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on >>> not-so-huge modes >>> >>> The default behavior is still the same. >>> >>> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> >> >> Yeah, I like this. I'll sign up Todd to review this all. > > I guess we'll go with this then, but I'll step back from this particular > patch for a bit, and share my concerns over module parameters and > quirks. > > I am generally opposed to adding module parameters or quirks to > workaround issues in features that should just work. They are an easy > way out for things we should root cause and fix properly. > > Do not mistake me for an idealist for thinking this way, as I'm being > pragmatic. > > The people who report bugs to us are roughly the same people who are > capable of setting the module parameter. Once they figure that out, > they'll stop responding to our requests for testing and info. We've seen > this happen before. We'd hurt our chances of making things work out of > the box for the average user. > > The more we add module parameters, the combinations of them > explode. Debugging *other* problems becomes harder. In the bugs I work > on, the #1 request I have is full dmesg, partially because I want to see > all the wild kernel parameters the user might have set. And all too > often they have. When there are module parameters that fix some bugs, > the blogs and forums get filled with tips about them, and people use > them, whether they strictly have the same bug or not. Search for i915 > invert brightness for example. > > It's also not easy to drop module parameters after we've added them. You > know the drill. Even after we've fixed everything the module parameter > was supposed to fix, dropping it leads to https://xkcd.com/1172/. Hi I totally understand your point and I agree that your concerns are valid. But OTOH the patch could substantially improve the lives of our users, and it allow allows much easier debugging for the developers. So I really think there's a tradeoff between "making it easier for users" vs "hiding bugs" vs "making it easier to debug". In the ideal world, we will make the default parameter work for everybody, and that will be the only option. But while that's not the case, we could at least try to make something better. I also remember the RC6 case, where the addition of the Kernel parameter allowed more people to actually test RC6 and report the problems, and in the end we finally fixed the remaining issue that was preventing RC6 from being enabled by default. But yes, we still have people that use RC6 parameters values they are not supposed to use, but OTOH we also have users who can enable RC6 on ILK without any problems. I wrote this patch for my own debugging purposes, and it was very useful to my development efforts. I have quite a few panels here, and I was trying to find a panel that doesn't work with either "wide and slow" or "narrow and fast", so the command-line option allowed me to quickly replace panels and retry. I also found a panel that doesn't work at all, and the finer-grained option allowed me to test it. I also have written other similar debug options in the past, that I never sent to the mailing list. For example, I have local patches that allow me to choose a different policy for the panel power sequencing registers: I wrote these when I noticed that, in a Mac machine, the power sequencing values set on boot were completely different from the ones set on the VBT, and the values chosen by our driver were the slowest of both worlds. So I guess this discussion is a nice opportunity for us to reach a general conclusion on what is the policy we should adopt for adding parameters that allow better debugging. Maybe if we had a way to specify that some parameters are strictly for debugging, or that some parameters are expected to break user's machines... Anyway, I can discard the patch if we want. I can also remove the option to arbitrarily force a given bw+lane configuration. I also found a bug on my own patch (missing "break" statement), so I need to send V2 anyway. Thanks, Paulo > > > BR, > Jani. > > > -- > Jani Nikula, Intel Open Source Technology Center
On Fri, Apr 25, 2014 at 02:48:07PM -0300, Paulo Zanoni wrote: > 2014-04-25 6:00 GMT-03:00 Jani Nikula <jani.nikula@linux.intel.com>: > > On Fri, 25 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote: > >> On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote: > >>> From: Paulo Zanoni <paulo.r.zanoni@intel.com> > >>> > >>> We still have way too many bugs with DP link training. We keep > >>> switching between "narrow and fast" and "wide and slow", we recently > >>> added 5GHz support, and whenever there's a bug report, we have to ask > >>> people to apply patches and test them. > >>> > >>> Wouldn't it be so much better if we could just ask them to boot with > >>> some specific Kernel boot option instead of applying a patch? This > >>> will move the situation from "i915.ko is completely broken!" to > >>> "i915.ko's default values are broken, but there's an option I can set > >>> to fix it, so I won't need to learn how to compile a Kernel!". > >>> > >>> Some useful values: > >>> - i915.dp_link_train_policy=1 for "wide and slow" > >>> - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes, > >>> which should be able to fit 1920x1080@60Hz and 24bpp > >>> - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on > >>> not-so-huge modes > >>> > >>> The default behavior is still the same. > >>> > >>> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> > >> > >> Yeah, I like this. I'll sign up Todd to review this all. > > > > I guess we'll go with this then, but I'll step back from this particular > > patch for a bit, and share my concerns over module parameters and > > quirks. > > > > I am generally opposed to adding module parameters or quirks to > > workaround issues in features that should just work. They are an easy > > way out for things we should root cause and fix properly. > > > > Do not mistake me for an idealist for thinking this way, as I'm being > > pragmatic. > > > > The people who report bugs to us are roughly the same people who are > > capable of setting the module parameter. Once they figure that out, > > they'll stop responding to our requests for testing and info. We've seen > > this happen before. We'd hurt our chances of making things work out of > > the box for the average user. > > > > The more we add module parameters, the combinations of them > > explode. Debugging *other* problems becomes harder. In the bugs I work > > on, the #1 request I have is full dmesg, partially because I want to see > > all the wild kernel parameters the user might have set. And all too > > often they have. When there are module parameters that fix some bugs, > > the blogs and forums get filled with tips about them, and people use > > them, whether they strictly have the same bug or not. Search for i915 > > invert brightness for example. > > > > It's also not easy to drop module parameters after we've added them. You > > know the drill. Even after we've fixed everything the module parameter > > was supposed to fix, dropping it leads to https://xkcd.com/1172/. > > Hi > > I totally understand your point and I agree that your concerns are > valid. But OTOH the patch could substantially improve the lives of our > users, and it allow allows much easier debugging for the developers. > So I really think there's a tradeoff between "making it easier for > users" vs "hiding bugs" vs "making it easier to debug". In the ideal > world, we will make the default parameter work for everybody, and that > will be the only option. But while that's not the case, we could at > least try to make something better. I also remember the RC6 case, > where the addition of the Kernel parameter allowed more people to > actually test RC6 and report the problems, and in the end we finally > fixed the remaining issue that was preventing RC6 from being enabled > by default. But yes, we still have people that use RC6 parameters > values they are not supposed to use, but OTOH we also have users who > can enable RC6 on ILK without any problems. > > I wrote this patch for my own debugging purposes, and it was very > useful to my development efforts. I have quite a few panels here, and > I was trying to find a panel that doesn't work with either "wide and > slow" or "narrow and fast", so the command-line option allowed me to > quickly replace panels and retry. I also found a panel that doesn't > work at all, and the finer-grained option allowed me to test it. > > I also have written other similar debug options in the past, that I > never sent to the mailing list. For example, I have local patches that > allow me to choose a different policy for the panel power sequencing > registers: I wrote these when I noticed that, in a Mac machine, the > power sequencing values set on boot were completely different from the > ones set on the VBT, and the values chosen by our driver were the > slowest of both worlds. > > So I guess this discussion is a nice opportunity for us to reach a > general conclusion on what is the policy we should adopt for adding > parameters that allow better debugging. Maybe if we had a way to > specify that some parameters are strictly for debugging, or that some > parameters are expected to break user's machines... > > Anyway, I can discard the patch if we want. I can also remove the > option to arbitrarily force a given bw+lane configuration. > > I also found a bug on my own patch (missing "break" statement), so I > need to send V2 anyway. Imo for anything related to modesetting or which needs to be set at driver load we want module options - for users it's really hard to set something in debugfs with a black screen. But we also want to ensure that users to play around with this for fun, so I'll work on the debug module option thing a bit more. -Daniel
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 7d6acb4..d5ae8dc 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -1941,6 +1941,7 @@ struct i915_params { bool reset; bool disable_display; bool disable_vtd_wa; + int dp_link_train_policy; }; extern struct i915_params i915 __read_mostly; diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c index d05a2af..8c358e7 100644 --- a/drivers/gpu/drm/i915/i915_params.c +++ b/drivers/gpu/drm/i915/i915_params.c @@ -48,6 +48,7 @@ struct i915_params i915 __read_mostly = { .disable_display = 0, .enable_cmd_parser = 1, .disable_vtd_wa = 0, + .dp_link_train_policy = 0, }; module_param_named(modeset, i915.modeset, int, 0400); @@ -156,3 +157,10 @@ MODULE_PARM_DESC(disable_vtd_wa, "Disable all VT-d workarounds (default: false)" module_param_named(enable_cmd_parser, i915.enable_cmd_parser, int, 0600); MODULE_PARM_DESC(enable_cmd_parser, "Enable command parsing (1=enabled [default], 0=disabled)"); + +module_param_named(dp_link_train_policy, i915.dp_link_train_policy, int, 0600); +MODULE_PARM_DESC(dp_link_train_policy, + "Choose strategy for DP link training " + "(0=narrow and fast [default], 1=wide and slow. For other values, " + "bits 11:8 are for the BW and bits 7:4 are for the nubmer of lanes, " + "check intel_dp_compute_link_config() for more details.)"); diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c index 884166b..25f7e1c 100644 --- a/drivers/gpu/drm/i915/intel_dp.c +++ b/drivers/gpu/drm/i915/intel_dp.c @@ -800,11 +800,42 @@ static bool intel_dp_compute_link_config(int mode_clock, int bpp, mode_rate = intel_dp_link_required(mode_clock, bpp); - for (lanes = min_lanes; lanes <= max_lanes; lanes <<= 1) + switch (i915.dp_link_train_policy) { + case 0: /* Narrow and fast. */ + for (lanes = min_lanes; lanes <= max_lanes; lanes <<= 1) + for (bw_it = min_bw_index; bw_it <= max_bw_index; + bw_it++) + if (link_config_is_possible(mode_rate, lanes, + bws[bw_it])) + goto found; + case 1: /* Wide and slow. */ for (bw_it = min_bw_index; bw_it <= max_bw_index; bw_it++) - if (link_config_is_possible(mode_rate, lanes, - bws[bw_it])) - goto found; + for (lanes = min_lanes; lanes <= max_lanes; lanes <<= 1) + if (link_config_is_possible(mode_rate, lanes, + bws[bw_it])) + goto found; + default: /* Bits 11:8 contain the index of the bws array. + * Bits 7:4 contain the number of lanes. + * Example: i915.dp_link_train_policy=0x140 uses + * DP_LINK_BW_2_7 and 4 lanes. */ + bw_it = (i915.dp_link_train_policy >> 8) & 0xF; + lanes = (i915.dp_link_train_policy >> 4) & 0xF; + + if (bw_it < min_bw_index || bw_it > max_bw_index) { + DRM_ERROR("Invalid BW index\n"); + return false; + } + + if (lanes < min_lanes || lanes > max_lanes || + /* Not a power of two. */ + !(lanes != 0 && (lanes & (lanes - 1)) == 0)) { + DRM_ERROR("Invalid number of lanes.\n"); + return false; + } + + if (link_config_is_possible(mode_rate, lanes, bws[bw_it])) + goto found; + } return false;