On Thu, Oct 17, 2019 at 7:19 AM Uwe Kleine-König u.kleine-koenig@pengutronix.de wrote:
On Thu, Oct 17, 2019 at 12:47:27PM +0100, Daniel Thompson wrote:
On Thu, Oct 17, 2019 at 10:10:59AM +0200, Uwe Kleine-König wrote:
A previous change in the pwm core (namely 01ccf903edd6 ("pwm: Let pwm_get_state() return the last implemented state")) changed the semantic of pwm_get_state() and disclosed an (as it seems) common problem in lowlevel PWM drivers. By not relying on the period and duty cycle being retrievable from a disabled PWM this type of problem is worked around.
Apart from this issue only calling the pwm_get_state/pwm_apply_state combo once is also more effective.
I'm only interested in the second paragraph here.
There seems to be a reasonable consensus that the i.MX27 and cros-ec PWM drivers should be fixed for the benefit of other PWM clients. So we make this change because it makes the pwm-bl better... not to work around bugs ;-).
That's fine, still I think it's fair to explain the motivation of creating this patch.
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 746eebc411df..ddebd62b3978 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -67,40 +62,27 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
static void pwm_backlight_power_off(struct pwm_bl_data *pb) {
- struct pwm_state state;
- pwm_get_state(pb->pwm, &state);
- if (!pb->enabled)
return;Why remove the pb->enabled check? I thought that was there to ensure we don't mess up the regular reference counts.
I havn't looked yet, but I guess I have to respin. Expect a v2 later today.
I would agree that a high-level fix is better than a series of low level driver fixes. For what its worth, your V1 patch worked fine on my i.MX6Q. I can test the V2 patch when its ready.
adam
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |