[Intel-gfx] [PATCH v2 09/15] pwm: crc: Enable/disable PWM output on enable/disable

[Hans de Goede]

Hi,

On 6/12/20 12:20 AM, Uwe Kleine-König wrote:
> On Sun, Jun 07, 2020 at 08:18:34PM +0200, Hans de Goede wrote:
>> The pwm-crc code is using 2 different enable bits:
>> 1. bit 7 of the PWM0_CLK_DIV (PWM_OUTPUT_ENABLE)
>> 2. bit 0 of the BACKLIGHT_EN register
>>
>> So far we've kept the PWM_OUTPUT_ENABLE bit set when disabling the PWM,
>> this commit makes crc_pwm_disable() clear it on disable and makes
>> crc_pwm_enable() set it again on re-enable.
>>
>> This should disable the internal (divided) PWM clock and tri-state the
>> PWM output pin when disabled, saving some power.
> 
> It would be great if you could also document that disabling the PWM
> makes the output tri-state. There are a few drivers that have a
> "Limitations" section at their top. Describing that there (in the same
> format) would be the right place.
> 
> Also note that according to Thierry's conception getting a (driven)
> inactive output is the right thing for a disabled PWM.

Hmm, the tri-state thing is an assumption from my side and we
don't have any docs for this PWM controller, so I'm not sure at
all if that is true. So I think it will be better to just drop
the tri-state bit from the commit msg for the next version.

Regards,

Hans