[Dropped Bartlomiej Zolnierkiewicz from Cc:; my mailer daemon claims the email address doens't exist.] Hello Guenter, On Fri, May 06, 2022 at 07:12:44AM -0700, Guenter Roeck wrote: > On Fri, May 06, 2022 at 02:23:11PM +0200, Alexander Stein wrote: > > Am Freitag, 6. Mai 2022, 12:23:01 CEST schrieb Uwe Kleine-König: > > > See > > > https://lore.kernel.org/linux-pwm/20180806155129.cjcc7okmwtaujf43@xxxxxxxxxxxxxx/ > > > for one of the previous discussions. > > > > Thanks for the link. I took a look into it. I'm on your side here, IMHO > > pwm_disable() implies that the PWM perphery is disabled, including any clocks > > or powerdomain. This is what pwm-imx27 actually does. This might lead to a, > > probably platform dependent, (undefined?) state of the PWM output pin. > > This implies it is not possible to disable the PWM periphery for inverted > > signals, if the disabled state is not the inactive level. You know all about > > it already. > > Then again from pwm-fan side I want be able to disable the FAN, turning of > > regulator and PWM, so powersaving is possible. That's what this patch is > > about. This is similar also what pwm_bl is doing. > > Independent of the exact semantics, it makes sense to disable the regulator in > > pwm-fan as well when the fan shall be disabled. > > There are fans which never stop if pwm==0, such as some CPU fans. I don't I assume with pwm==0 you actually mean duty_cycle == 0? > think it is a good idea to force those off by turning off their power. The > problem in the driver is that it treats pwm==0 as "disable pwm", not as > "set pwm output to 0", Part of the probem may be that the ABI doesn't have > a good representation for "disable pwm output", which is what is really > wanted/needed here. Disable pwm output == set pwm output to High-Z? Not all PWMs are able to provide that. > I think the best solution would be to implement and > use pwmX_enable, and define in the driver documentation that pwm1_enable=0 > reflects "disable pwm" and pwm1_enable=1 reflects "emable manual pwm > control:. At the same time, stop associating "pwm==0" with "disable pwm", > but just set the pwm output value to 0. Are you talking about the PWM framework here, or only the pwm-fan driver? I'd expect there are better names than pwm1_enable for the intended semantic. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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