Hello,
On Wed, Jun 30, 2021 at 12:22:22PM +0200, Geert Uytterhoeven wrote:
> Hi Uwe,
>
> On Wed, Jun 30, 2021 at 8:48 AM Uwe Kleine-König
> <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> > On Tue, Jun 29, 2021 at 09:44:38PM +0200, Geert Uytterhoeven wrote:
> > > On Sat, 1 May 2021, Uwe Kleine-König wrote:
> > > > Without this change it can happen that if changing the polarity succeeded
> > > > but changing duty_cycle and period failed pwm->state contains a mixture
> > > > between the old and the requested state.
> > > >
> > > > So remember the initial state before starting to modify the configuration
> > > > and restore it when one of the required callback fails.
> > > >
> > > > Compared to the previous implementation .disable() (if necessary) is called
> > > > earlier to prevent a glitch.
> > > >
> > > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > >
> > > Thanks for your patch, which is now commit d7bff84fe7ed8c3b ("pwm:
> > > Ensure for legacy drivers that pwm->state stays consistent") in
> > > pwm/for-next.
> > >
> > > This commit broke the backlight on the Atmark Techno Armadillo 800 EVA
> > > board (arch/arm/boot/dts/r8a7740-armadillo800eva.dts), which now shows a
> > > black screen. Reverting the commit fixes the problem.
> > >
> > > Do you have an idea what is wrong, and how to fix it?
> >
> > I starred at the patch for some time now and couldn't find a problem.
> > Looking at drivers/pwm/pwm-renesas-tpu.c I don't see something obvious.
> > (The .set_polarity callback is faulty as I doesn't commit the request to
> > hardware, but that shouldn't matter here.)
> >
> > I guess the first request the backlight driver emits is
> >
> > .period = 33333,
> > .duty_cycle = 33333,
> > .enabled = true,
> > .polarity = PWM_POLARITY_INVERSED,
> >
> > which should result into the following driver calls (with and without
> > the breaking commit):
> >
> > tpu_pwm_set_polarity(chip, pwm, PWM_POLARITY_INVERSED);
> > tpu_pwm_config(chip, pwm, 33333, 33333);
> > tpu_pwm_enable(chip, pwm);
> >
> > Can you confirm that?
>
> tpu_pwm_config() is no longer called:
>
> renesas-tpu-pwm e6600000.pwm: tpu_pwm_set_polarity:334: channel
> 2, polarity = 1
> -renesas-tpu-pwm e6600000.pwm: tpu_pwm_config:257: channel = 2,
> duty_ns = 0, period_ns = 33333
> -renesas-tpu-pwm e6600000.pwm: tpu_pwm_config:257: channel = 2,
> duty_ns = 33333, period_ns = 33333
> renesas-tpu-pwm e6600000.pwm: tpu_pwm_enable:346: channel 2
OK, I see a problem (though this doesn't explain the display staying
off directly after boot):
After doing:
pwm_apply_state(pwm, { .period = 33333, .duty_cycle = 0, .enabled = false, .polarity = ..});
.period and .duty_cycle are assumed to be set even though calling
->config was skipped because .enabled is false.
So when
pwm_apply_state(pwm, { .period = 33333, .duty_cycle = 0, .enabled = true, .polarity = ..});
is called next, ->config isn't called because the core assumes
.duty_cycle and .period are already setup fine.
So we either must not skip calling ->config when .enabled is false:
diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index ab38627bcacd..f8a5a095a410 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -558,12 +558,8 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm,
pwm->state.polarity = state->polarity;
}
- if (!state->enabled) {
- if (pwm->state.enabled)
- chip->ops->disable(chip, pwm);
-
- return 0;
- }
+ if (!state->enabled && pwm->state.enabled)
+ chip->ops->disable(chip, pwm);
if (state->period != pwm->state.period ||
state->duty_cycle != pwm->state.duty_cycle) {
@@ -577,7 +573,7 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm,
pwm->state.duty_cycle = state->duty_cycle;
}
- if (!pwm->state.enabled) {
+ if (state->enabled && !pwm->state.enabled) {
err = chip->ops->enable(chip, pwm);
if (err)
goto rollback;
or we have to call ->config unconditionally:
diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index ab38627bcacd..05d7afe25b42 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -565,17 +565,21 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm,
return 0;
}
+ /*
+ * We cannot skip this even if state->period == pwm->state.period &&
+ * state->duty_cycle == pwm->state.duty_cycle because we might have
+ * exited early in the last call to pwm_apply_state because of
+ * !state->enabled and so the two values in pwm->state might not be
+ * configured in hardware.
+ */
+ err = chip->ops->config(pwm->chip, pwm,
+ state->duty_cycle,
+ state->period);
+ if (err)
+ goto rollback;
+
+ pwm->state.period = state->period;
+ pwm->state.duty_cycle = state->duty_cycle;
- if (state->period != pwm->state.period ||
- state->duty_cycle != pwm->state.duty_cycle) {
- err = chip->ops->config(pwm->chip, pwm,
- state->duty_cycle,
- state->period);
- if (err)
- goto rollback;
-
- pwm->state.period = state->period;
- pwm->state.duty_cycle = state->duty_cycle;
- }
if (!pwm->state.enabled) {
err = chip->ops->enable(chip, pwm);
I slightly prefer the latter patch, but if this is indeed your problem
both should fix it for you.
Can you give that a try please?
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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