Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sun, 16 Dec 2018 15:18:52 +0100 | From | Paul Cercueil <> | Subject | Re: [PATCH v8 15/26] pwm: jz4740: Add support for the JZ4725B |
| |
Hi,
Le ven. 14 déc. 2018 à 15:26, Uwe Kleine-König <u.kleine-koenig@pengutronix.de> a écrit : > Hello, > > On Fri, Dec 14, 2018 at 02:50:20PM +0100, Linus Walleij wrote: >> On Thu, Dec 13, 2018 at 9:42 PM Uwe Kleine-König >> <u.kleine-koenig@pengutronix.de> wrote: >> > [Adding Linus Walleij to Cc:] >> > On Thu, Dec 13, 2018 at 03:03:15PM +0100, Paul Cercueil wrote: >> > > Le jeu. 13 déc. 2018 à 10:24, Uwe Kleine-König >> > > <u.kleine-koenig@pengutronix.de> a écrit : >> > > > On Wed, Dec 12, 2018 at 11:09:10PM +0100, Paul Cercueil wrote: >> > > > > The PWM in the JZ4725B works the same as in the JZ4740, >> except that >> > > > > it >> > > > > only has 6 channels available instead of 8. >> > > > >> > > > this driver is probed only from device tree? If yes, it might >> be >> > > > sensible to specify the number of PWMs there and get it from >> there. >> > > > There doesn't seem to be a generic binding for that, but >> there are >> > > > several drivers that could benefit from it. (This is a bigger >> project >> > > > though and shouldn't stop your patch. Still more as it >> already got >> > > > Thierry's ack.) >> > > >> > > I think there needs to be a proper guideline, as there doesn't >> seem to be >> > > a consensus about this. I learned from emails with Rob and >> Linus (Walleij) >> > > that I should not have in devicetree what I can deduce from the >> compatible >> > > string. >> > >> > I understood them a bit differently. It is ok to deduce things >> from the >> > compatible string. But if you define a generic property (say) >> "num-pwms" >> > that is used uniformly in most bindings this is ok, too. (And >> then the >> > two different devices could use the same compatible.) >> > >> > An upside of the generic "num-pwms" property is that the pwm core >> could >> > sanity check pwm phandles before passing them to the hardware >> drivers. >> >> I don't know if this helps, but in GPIO we have "ngpios" which is >> used to augment an existing block as to the number of lines actually >> used with it. >> >> The typical case is that an ASIC engineer synthesize a block for >> 32 GPIOs but only 12 of them are routed to external pads. So >> we augment the behaviour of that driver to only use 12 of the >> 32 lines. >> >> I guess using the remaining 20 lines "works" in a sense but they >> have no practical use and will just bias electrons in the silicon >> for no use. > > This looks very similar to the case under discussion. > >> So if the PWM case is something similar, then by all means add >> num-pwms. > > .. or "npwms" to use the same nomenclature as the gpio binding?
If we're going to do something like this, should it be the drivers or the core (within pwmchip_add) that checks for this "npwms" property?
> Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König > | > Industrial Linux Solutions | > http://www.pengutronix.de/ |
| ![\](/images/icornerr.gif) |