On Thu, Nov 08, 2018 at 03:21:44PM +0000, Vokáč Michal wrote: > On 7.11.2018 16:01, Uwe Kleine-König wrote: [...] > > For both the solution is to let the bootloader enable the pwm with > > the right output level. Am I missing something? > > Bootloader is only a small part of the whole solution I think. And I > suppose you meant: "enable the *GPIO* with the right output level". > > - Even if you use GPIO in bootloader to set the required level the > time frame from imx_pwm_probe to imx_pwm_apply is not covered. > > - Currently there is no support in Linux pwm-imx driver to detect > the PWM chip is already enabled at probe time. I actually send > patches for this a month ago [1]. No response yet. > > - Inverted PWM does not work in U-Boot (on imx at least). And it > does not seam like it can be fixed easily. I do not know what is > the situation in other bootloaders. > > So my current bootloader solution is one of: > - Set the pin to the appropriate (HIGH) level using GPIO. > - Do not touch the pin at all, it has 100k pull-up by default. First of all, I don't think we should rely on any bootloader setting up things properly. I already said elsewhere that the reset defaults will likely already be such that the PWM outputs zero power (i.e. high for inversed PWM). Michal's comments above seem to suggest that this is indeed the case. If the pin is 100k pull-up by default (I assume that means on reset), then that's exactly what I would expect for this kind of pin. And that's also an excellent pin state for the kernel to use when it no longer needs to actively drive the PWM. That means on pwm_disable() we can simply revert to the 100k pull-up default and let the PWM pin be in the very same state that it is on reset. Can't get any better than that. So really, I think the only proper solution to this problem is to get pinctrl involved and configure the pin as PWM when it is actively used, and change it back to 100k pull-up otherwise. And, yes, I understand that this slightly complicates the driver, but it's really the right thing to do and it fixes all known issues, and to me that's clear evidence that it is the right solution and therefore definitely worth the added complexity. Thierry
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