| Message ID | 1411512625-10657-1-git-send-email-joe.konno@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 2014-09-23 at 15:50 -0700, Joe Konno wrote: > From: Joe Konno <joe.konno@intel.com> > > Improper integer division-- truncated rather than rounded-- in the > scale() function causes actual_brightness != brightness. This (partial) > work-around should be sufficient for a majority of use-cases, but it is > by no means a complete solution. > > TODO: Determine how best to scale "user" values to "hw" values, and > vice-versa, when the ranges are of different sizes. That would be a > buggy scenario even with this work-around. > > The issue was introduced in the following (v3.17-rc1) commit: > > 6dda730 drm/i915: respect the VBT minimum backlight brightness > Reviewed-by: U. Artie Eoff <ullysses.a.eoff@intel.com> > Signed-off-by: Joe Konno <joe.konno@intel.com> > --- > drivers/gpu/drm/i915/intel_panel.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c > index f17ada3..c40f837 100644 > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -421,7 +421,8 @@ static uint32_t scale(uint32_t source_val, > /* avoid overflows */ > target_val = (uint64_t)(source_val - source_min) * > (target_max - target_min); > - do_div(target_val, source_max - source_min); > + target_val = (target_val + ((source_max - source_min) / 2)) / > + (source_max - source_min); > target_val += target_min; > > return target_val;
On Tue, Sep 23, 2014 at 03:50:25PM -0700, Joe Konno wrote: > From: Joe Konno <joe.konno@intel.com> > > Improper integer division-- truncated rather than rounded-- in the That's confusing. It reads that you are converting to using truncated, rather than to rounding. > scale() function causes actual_brightness != brightness. This (partial) > work-around should be sufficient for a majority of use-cases, but it is > by no means a complete solution. > > TODO: Determine how best to scale "user" values to "hw" values, and > vice-versa, when the ranges are of different sizes. That would be a > buggy scenario even with this work-around. > > The issue was introduced in the following (v3.17-rc1) commit: > > 6dda730 drm/i915: respect the VBT minimum backlight brightness > > Signed-off-by: Joe Konno <joe.konno@intel.com> > --- > drivers/gpu/drm/i915/intel_panel.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c > index f17ada3..c40f837 100644 > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -421,7 +421,8 @@ static uint32_t scale(uint32_t source_val, > /* avoid overflows */ > target_val = (uint64_t)(source_val - source_min) * > (target_max - target_min); > - do_div(target_val, source_max - source_min); > + target_val = (target_val + ((source_max - source_min) / 2)) / > + (source_max - source_min); target_val = DIV_ROUND_CLOSEST(target_val, source_max - source_min); > target_val += target_min; > > return target_val;
Many thanks, Chris. I'll incorporate your feedback into v2. On 09/23/2014 11:04 PM, Chris Wilson wrote: > On Tue, Sep 23, 2014 at 03:50:25PM -0700, Joe Konno wrote: >> From: Joe Konno <joe.konno@intel.com> >> >> Improper integer division-- truncated rather than rounded-- in the > That's confusing. It reads that you are converting to using truncated, > rather than to rounding. > >> scale() function causes actual_brightness != brightness. This (partial) >> work-around should be sufficient for a majority of use-cases, but it is >> by no means a complete solution. >> >> TODO: Determine how best to scale "user" values to "hw" values, and >> vice-versa, when the ranges are of different sizes. That would be a >> buggy scenario even with this work-around. >> >> The issue was introduced in the following (v3.17-rc1) commit: >> >> 6dda730 drm/i915: respect the VBT minimum backlight brightness >> >> Signed-off-by: Joe Konno <joe.konno@intel.com> >> --- >> drivers/gpu/drm/i915/intel_panel.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c >> index f17ada3..c40f837 100644 >> --- a/drivers/gpu/drm/i915/intel_panel.c >> +++ b/drivers/gpu/drm/i915/intel_panel.c >> @@ -421,7 +421,8 @@ static uint32_t scale(uint32_t source_val, >> /* avoid overflows */ >> target_val = (uint64_t)(source_val - source_min) * >> (target_max - target_min); >> - do_div(target_val, source_max - source_min); >> + target_val = (target_val + ((source_max - source_min) / 2)) / >> + (source_max - source_min); > target_val = DIV_ROUND_CLOSEST(target_val, source_max - source_min); > >> target_val += target_min; >> >> return target_val;
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index f17ada3..c40f837 100644 --- a/drivers/gpu/drm/i915/intel_panel.c +++ b/drivers/gpu/drm/i915/intel_panel.c @@ -421,7 +421,8 @@ static uint32_t scale(uint32_t source_val, /* avoid overflows */ target_val = (uint64_t)(source_val - source_min) * (target_max - target_min); - do_div(target_val, source_max - source_min); + target_val = (target_val + ((source_max - source_min) / 2)) / + (source_max - source_min); target_val += target_min; return target_val;