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@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx> 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? Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |
