On Thu, Sep 03, 2020 at 12:51:03PM +0200, Hans de Goede wrote: > Before this commit pwm_lpss_apply() was making 2 assuming > 2 pre-conditions were met by the existing hardware state: I think that "making 2" is too much. > > 1. That the base-unit and on-time-div read back from the > control register are those actually in use, so that it > can skip setting the update bit if the read-back value > matches the desired values. > > 2. That the controller is enabled when the cached > pwm_state.enabled says that the controller is enabled. > > As the long history of fixes for subtle (often suspend/resume) > lpss-pwm issues shows, this assumptions are not necessary > always true. > > 1. Specifically is not true on some (*) Cherry Trail devices > with a nasty GFX0._PS3 method which: a. saves the ctrl reg value. > b. sets the base-unit to 0 and writes the update bit to apply/commit > c. restores the original ctrl value without setting the update bit, > so that the 0 base-unit value is still in use. > > 2. Assumption 2. currently is true, but only because of the code which > saves/restores the state on suspend/resume. By convention restoring the > PWM state should be done by the PWM consumer and the presence of this > code in the pmw-lpss driver is a bug. Therefor the save/restore code will > be dropped in the next patch in this series, after which this assumption > also is no longer true. > > This commit changes the pwm_lpss_apply() to make any assumptions about the Did you mean to say "... to _not_ make any assumptions ..."? > state the hardware is in. Instead it makes pwm_lpss_apply() always fully > program the PWM controller, making it much less fragile. > > *) Seen on the Acer One 10 S1003, Lenovo Ideapad Miix 310 and 320 models > and various Medion models. > > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> > --- > drivers/pwm/pwm-lpss.c | 21 +++++++++------------ > 1 file changed, 9 insertions(+), 12 deletions(-) Other than the two small nits, this looks much more idiomatic and true to the atomic API, so: Acked-by: Thierry Reding <thierry.reding@xxxxxxxxx>
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