| Message ID | 20210226141411.2517368-2-linux@rasmusvillemoes.dk (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
| Series | add ripple counter dt binding and driver | expand |
On Fri, Feb 26, 2021 at 03:14:10PM +0100, Rasmus Villemoes wrote: > While a ripple counter can not usually be interfaced with (directly) > from software, it may still be a crucial component in a board > layout. To prevent its input clock from being disabled by the clock > core because it apparently has no consumer, one needs to be able to > represent that consumer in DT. I'm okay with this as it is describing h/w, but we already 'protected-clocks' property which should work. > > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> > --- > Documentation/devicetree/bindings/misc/ripple-ctr.txt | 8 ++++++++ > 1 file changed, 8 insertions(+) > create mode 100644 Documentation/devicetree/bindings/misc/ripple-ctr.txt > > diff --git a/Documentation/devicetree/bindings/misc/ripple-ctr.txt b/Documentation/devicetree/bindings/misc/ripple-ctr.txt > new file mode 100644 > index 000000000000..1497d3a237a7 > --- /dev/null > +++ b/Documentation/devicetree/bindings/misc/ripple-ctr.txt > @@ -0,0 +1,8 @@ > +Generic ripple counter > + > +A ripple counter is a simple component that can for example be used to > +delay propagation of a signal. > + > +Required properties: > +- compatible: Must be "linux,ripple-ctr". Nothing linux specific about this. > +- clocks: Input clock specifier. Refer to common clock bindings. > -- > 2.29.2 >
On 08/03/2021 18.21, Rob Herring wrote: > On Fri, Feb 26, 2021 at 03:14:10PM +0100, Rasmus Villemoes wrote: >> While a ripple counter can not usually be interfaced with (directly) >> from software, it may still be a crucial component in a board >> layout. To prevent its input clock from being disabled by the clock >> core because it apparently has no consumer, one needs to be able to >> represent that consumer in DT. > > I'm okay with this as it is describing h/w, but we already > 'protected-clocks' property which should work. Hm. Unless https://lore.kernel.org/lkml/20200903040015.5627-2-samuel@sholland.org/ gets merged, I don't see how this would work out-of-the-box. Note that I sent a completely different v2, which made the gpio-wdt the clock consumer based on feedback from Guenter and Arnd, but that v2 isn't suitable for our case because it post-poned handling of the watchdog till after i2c is ready, which is too late. Somewhat similar to https://lore.kernel.org/lkml/20210222171247.97609-2-sebastian.reichel@collabora.com/ it seems. >> + >> +Required properties: >> +- compatible: Must be "linux,ripple-ctr". > > Nothing linux specific about this. True, but I was following the lead of the existing gpio-wdt binding. Is there some other "vendor" name one can and should use for completely generic and simple components like these? "generic"? Rasmus
On Mon, Mar 08, 2021 at 09:02:29PM +0100, Rasmus Villemoes wrote: > On 08/03/2021 18.21, Rob Herring wrote: > > On Fri, Feb 26, 2021 at 03:14:10PM +0100, Rasmus Villemoes wrote: > >> While a ripple counter can not usually be interfaced with (directly) > >> from software, it may still be a crucial component in a board > >> layout. To prevent its input clock from being disabled by the clock > >> core because it apparently has no consumer, one needs to be able to > >> represent that consumer in DT. > > > > I'm okay with this as it is describing h/w, but we already > > 'protected-clocks' property which should work. > > Hm. Unless > https://lore.kernel.org/lkml/20200903040015.5627-2-samuel@sholland.org/ > gets merged, I don't see how this would work out-of-the-box. Hum, no really clear what the hold up is there given it seems it was asked for. Letting it sit for 5 months is certainly not the way to get it merged. Anyways, that's the kernel's problem, not mine as far as DT bindings are concerned. > > Note that I sent a completely different v2, which made the gpio-wdt the > clock consumer based on feedback from Guenter and Arnd, but that v2 > isn't suitable for our case because it post-poned handling of the > watchdog till after i2c is ready, which is too late. Somewhat similar to > https://lore.kernel.org/lkml/20210222171247.97609-2-sebastian.reichel@collabora.com/ > it seems. Now at that one in my queue... I think 'protected-clocks' is the best way to avoid any driver probe ordering issues. It's the only thing that really captures don't turn off this clock. The ripple counter binding doesn't really capture that or what it is related to. Also, the ripple-counter driver could be a module and you'd still have the same issue as v2. > >> + > >> +Required properties: > >> +- compatible: Must be "linux,ripple-ctr". > > > > Nothing linux specific about this. > > True, but I was following the lead of the existing gpio-wdt binding. Is > there some other "vendor" name one can and should use for completely > generic and simple components like these? "generic"? Most 'generic' and GPIO based interfaces have no vendor prefix. Rob
On 08/03/2021 22.38, Rob Herring wrote: > On Mon, Mar 08, 2021 at 09:02:29PM +0100, Rasmus Villemoes wrote: >> On 08/03/2021 18.21, Rob Herring wrote: >>> On Fri, Feb 26, 2021 at 03:14:10PM +0100, Rasmus Villemoes wrote: >>>> While a ripple counter can not usually be interfaced with (directly) >>>> from software, it may still be a crucial component in a board >>>> layout. To prevent its input clock from being disabled by the clock >>>> core because it apparently has no consumer, one needs to be able to >>>> represent that consumer in DT. >>> >>> I'm okay with this as it is describing h/w, but we already >>> 'protected-clocks' property which should work. >> >> Hm. Unless >> https://lore.kernel.org/lkml/20200903040015.5627-2-samuel@sholland.org/ >> gets merged, I don't see how this would work out-of-the-box. > > Hum, no really clear what the hold up is there given it seems it was > asked for. Letting it sit for 5 months is certainly not the way > to get it merged. Anyways, that's the kernel's problem, not mine as far > as DT bindings are concerned. > >> >> Note that I sent a completely different v2, which made the gpio-wdt the >> clock consumer based on feedback from Guenter and Arnd, but that v2 >> isn't suitable for our case because it post-poned handling of the >> watchdog till after i2c is ready, which is too late. Somewhat similar to >> https://lore.kernel.org/lkml/20210222171247.97609-2-sebastian.reichel@collabora.com/ >> it seems. > > Now at that one in my queue... I think 'protected-clocks' is the best > way to avoid any driver probe ordering issues. It's the only thing that > really captures don't turn off this clock. Agreed, and I did start by looking for a generic way to mark the clock as either "hands off, kernel" (relying on the bootloader to enable it), or better "make sure it's enabled". The closest I found was of_clk_detect_critical(), but the comment above that one says not to use it, so adding a call to some random RTC driver to support the clock-critical property just for my use case didn't seem like the right way to go. I didn't know about protected-clocks until you mentioned it, and it does seem to be the right way to handle these situations (which are apparently more common than I thought). The ripple counter binding > doesn't really capture that or what it is related to. Agreed, it was a "hail mary" and why I explained what I was really trying to achieve in the cover letter. Also, the > ripple-counter driver could be a module and you'd still have the same > issue as v2. Well, not quite. First of all, for a board like this, one always uses a tailor-made .config, where one would never set that to be a module (and even more obviously one wouldn't make the gpio-wdt driver a module). Second, it wouldn't be the same issue as v2. Rather, if the clock only gets enabled later when the ripple counter module would get loaded, there would be a period of time where the watchdog was rendered useless - the problem with v2 was that the watchdog wouldn't be petted in time, so the board would be reset before it booted completely. >>>> +Required properties: >>>> +- compatible: Must be "linux,ripple-ctr". >>> >>> Nothing linux specific about this. >> >> True, but I was following the lead of the existing gpio-wdt binding. Is >> there some other "vendor" name one can and should use for completely >> generic and simple components like these? "generic"? > > Most 'generic' and GPIO based interfaces have no vendor prefix. Ah, I see. Can we add just plain "wdt-gpio" to the gpio-wdt binding, and deprecate the "linux,wdt-gpio"? It's a little awkward to handle a "linux,wdt-gpio" compatible in a U-Boot driver. Rasmus
On Tue, Mar 9, 2021 at 12:39 AM Rasmus Villemoes <rasmus.villemoes@prevas.dk> wrote: > > On 08/03/2021 22.38, Rob Herring wrote: > > On Mon, Mar 08, 2021 at 09:02:29PM +0100, Rasmus Villemoes wrote: > >> On 08/03/2021 18.21, Rob Herring wrote: > >>> On Fri, Feb 26, 2021 at 03:14:10PM +0100, Rasmus Villemoes wrote: > >>>> While a ripple counter can not usually be interfaced with (directly) > >>>> from software, it may still be a crucial component in a board > >>>> layout. To prevent its input clock from being disabled by the clock > >>>> core because it apparently has no consumer, one needs to be able to > >>>> represent that consumer in DT. > >>> > >>> I'm okay with this as it is describing h/w, but we already > >>> 'protected-clocks' property which should work. > >> > >> Hm. Unless > >> https://lore.kernel.org/lkml/20200903040015.5627-2-samuel@sholland.org/ > >> gets merged, I don't see how this would work out-of-the-box. > > > > Hum, no really clear what the hold up is there given it seems it was > > asked for. Letting it sit for 5 months is certainly not the way > > to get it merged. Anyways, that's the kernel's problem, not mine as far > > as DT bindings are concerned. > > > >> > >> Note that I sent a completely different v2, which made the gpio-wdt the > >> clock consumer based on feedback from Guenter and Arnd, but that v2 > >> isn't suitable for our case because it post-poned handling of the > >> watchdog till after i2c is ready, which is too late. Somewhat similar to > >> https://lore.kernel.org/lkml/20210222171247.97609-2-sebastian.reichel@collabora.com/ > >> it seems. > > > > Now at that one in my queue... I think 'protected-clocks' is the best > > way to avoid any driver probe ordering issues. It's the only thing that > > really captures don't turn off this clock. > > Agreed, and I did start by looking for a generic way to mark the clock > as either "hands off, kernel" (relying on the bootloader to enable it), > or better "make sure it's enabled". The closest I found was > of_clk_detect_critical(), but the comment above that one says not to use > it, so adding a call to some random RTC driver to support the > clock-critical property just for my use case didn't seem like the right > way to go. > > I didn't know about protected-clocks until you mentioned it, and it does > seem to be the right way to handle these situations (which are > apparently more common than I thought). > > The ripple counter binding > > doesn't really capture that or what it is related to. > > Agreed, it was a "hail mary" and why I explained what I was really > trying to achieve in the cover letter. > > Also, the > > ripple-counter driver could be a module and you'd still have the same > > issue as v2. > > Well, not quite. First of all, for a board like this, one always uses a > tailor-made .config, where one would never set that to be a module (and > even more obviously one wouldn't make the gpio-wdt driver a module). Yes, I'd expect so in this case, but in general we really should try to avoid things dependent on being built-in (and ordering of initcalls). The whole notion of disabling resources in late_initcall is also kind of broken IMO and doesn't account for modules. > Second, it wouldn't be the same issue as v2. Rather, if the clock only > gets enabled later when the ripple counter module would get loaded, > there would be a period of time where the watchdog was rendered useless > - the problem with v2 was that the watchdog wouldn't be petted in time, > so the board would be reset before it booted completely. > > >>>> +Required properties: > >>>> +- compatible: Must be "linux,ripple-ctr". > >>> > >>> Nothing linux specific about this. > >> > >> True, but I was following the lead of the existing gpio-wdt binding. Is > >> there some other "vendor" name one can and should use for completely > >> generic and simple components like these? "generic"? > > > > Most 'generic' and GPIO based interfaces have no vendor prefix. > > Ah, I see. Can we add just plain "wdt-gpio" to the gpio-wdt binding, and > deprecate the "linux,wdt-gpio"? It's a little awkward to handle a > "linux,wdt-gpio" compatible in a U-Boot driver. No, just leave it. We have a few of these, but let's just not add new ones. In the end, it's just a string identifier. Rob
diff --git a/Documentation/devicetree/bindings/misc/ripple-ctr.txt b/Documentation/devicetree/bindings/misc/ripple-ctr.txt new file mode 100644 index 000000000000..1497d3a237a7 --- /dev/null +++ b/Documentation/devicetree/bindings/misc/ripple-ctr.txt @@ -0,0 +1,8 @@ +Generic ripple counter + +A ripple counter is a simple component that can for example be used to +delay propagation of a signal. + +Required properties: +- compatible: Must be "linux,ripple-ctr". +- clocks: Input clock specifier. Refer to common clock bindings.
While a ripple counter can not usually be interfaced with (directly) from software, it may still be a crucial component in a board layout. To prevent its input clock from being disabled by the clock core because it apparently has no consumer, one needs to be able to represent that consumer in DT. Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> --- Documentation/devicetree/bindings/misc/ripple-ctr.txt | 8 ++++++++ 1 file changed, 8 insertions(+) create mode 100644 Documentation/devicetree/bindings/misc/ripple-ctr.txt