On Tue, May 12, 2020 at 01:00:44PM +0200, Hans de Goede wrote:
Before commit cfc4c189bc70 ("pwm: Read initial hardware state at request time"), a driver's get_state callback would get called once per PWM from pwmchip_add().
pwm-lpss' runtime-pm code was relying on this, getting a runtime-pm ref for PWMs which are enabled at probe time from within its get_state callback, before enabling runtime-pm.
The change to calling get_state at request time causes a number of problems:
- PWMs enabled at probe time may get runtime suspended before they are
requested, causing e.g. a LCD backlight controlled by the PWM to turn off.
- When the request happens when the PWM has been runtime suspended, the
ctrl register will read all 1 / 0xffffffff, causing get_state to store bogus values in the pwm_state.
- get_state was using an async pm_runtime_get() call, because it assumed
that runtime-pm has not been enabled yet. If shortly after the request an apply call is made, then the pwm_lpss_is_updating() check may trigger because the resume triggered by the pm_runtime_get() call is not complete yet, so the ctrl register still reads all 1 / 0xffffffff.
This commit fixes these issues by moving the initial pm_runtime_get() call for PWMs which are enabled at probe time to the pwm_lpss_probe() function; and by making get_state take a runtime-pm ref before reading the ctrl reg.
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1828927 Fixes: cfc4c189bc70 ("pwm: Read initial hardware state at request time") Cc: stable@vger.kernel.org Signed-off-by: Hans de Goede hdegoede@redhat.com
drivers/pwm/pwm-lpss.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
Applied, thanks.
Thierry