| Message ID | 20230403133054.319070-3-angelogioacchino.delregno@collabora.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | pwm: mtk-disp: Fix backlight configuration at boot | expand |
On 03/04/2023 15:30, AngeloGioacchino Del Regno wrote: > The DISP_PWM controller's default behavior is to always use register > double buffering: all reads/writes are then performed on shadow > registers instead of working registers and this becomes an issue > in case our chosen configuration in Linux is different from the > default (or from the one that was pre-applied by the bootloader). > > An example of broken behavior is when the controller is configured > to use shadow registers, but this driver wants to configure it > otherwise: what happens is that the .get_state() callback is called > right after registering the pwmchip and checks whether the PWM is > enabled by reading the DISP_PWM_EN register; > At this point, if shadow registers are enabled but their content > was not committed before booting Linux, we are *not* reading the > current PWM enablement status, leading to the kernel knowing that > the hardware is actually enabled when, in reality, it's not. > > The aforementioned issue emerged since this driver was fixed with > commit 0b5ef3429d8f ("pwm: mtk-disp: Fix the parameters calculated > by the enabled flag of disp_pwm") making it to read the enablement > status from the right register. > > Configure the controller in the .get_state() callback to avoid > this desync issue and get the backlight properly working again. > > Fixes: 3f2b16734914 ("pwm: mtk-disp: Implement atomic API .get_state()") > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> > Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> > Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> > --- > drivers/pwm/pwm-mtk-disp.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c > index 82b430d881a2..fe9593f968ee 100644 > --- a/drivers/pwm/pwm-mtk-disp.c > +++ b/drivers/pwm/pwm-mtk-disp.c > @@ -196,6 +196,16 @@ static int mtk_disp_pwm_get_state(struct pwm_chip *chip, > return err; > } > > + /* > + * Apply DISP_PWM_DEBUG settings to choose whether to enable or disable > + * registers double buffer and manual commit to working register before > + * performing any read/write operation > + */ > + if (mdp->data->bls_debug) > + mtk_disp_pwm_update_bits(mdp, mdp->data->bls_debug, > + mdp->data->bls_debug_mask, > + mdp->data->bls_debug_mask); > + > rate = clk_get_rate(mdp->clk_main); > con0 = readl(mdp->base + mdp->data->con0); > con1 = readl(mdp->base + mdp->data->con1); Hi, Same test. Looks fine. Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com> Tested-by: Alexandre Mergnat <amergnat@baylibre.com> Regards, Alex
diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c index 82b430d881a2..fe9593f968ee 100644 --- a/drivers/pwm/pwm-mtk-disp.c +++ b/drivers/pwm/pwm-mtk-disp.c @@ -196,6 +196,16 @@ static int mtk_disp_pwm_get_state(struct pwm_chip *chip, return err; } + /* + * Apply DISP_PWM_DEBUG settings to choose whether to enable or disable + * registers double buffer and manual commit to working register before + * performing any read/write operation + */ + if (mdp->data->bls_debug) + mtk_disp_pwm_update_bits(mdp, mdp->data->bls_debug, + mdp->data->bls_debug_mask, + mdp->data->bls_debug_mask); + rate = clk_get_rate(mdp->clk_main); con0 = readl(mdp->base + mdp->data->con0); con1 = readl(mdp->base + mdp->data->con1);
The DISP_PWM controller's default behavior is to always use register double buffering: all reads/writes are then performed on shadow registers instead of working registers and this becomes an issue in case our chosen configuration in Linux is different from the default (or from the one that was pre-applied by the bootloader). An example of broken behavior is when the controller is configured to use shadow registers, but this driver wants to configure it otherwise: what happens is that the .get_state() callback is called right after registering the pwmchip and checks whether the PWM is enabled by reading the DISP_PWM_EN register; At this point, if shadow registers are enabled but their content was not committed before booting Linux, we are *not* reading the current PWM enablement status, leading to the kernel knowing that the hardware is actually enabled when, in reality, it's not. The aforementioned issue emerged since this driver was fixed with commit 0b5ef3429d8f ("pwm: mtk-disp: Fix the parameters calculated by the enabled flag of disp_pwm") making it to read the enablement status from the right register. Configure the controller in the .get_state() callback to avoid this desync issue and get the backlight properly working again. Fixes: 3f2b16734914 ("pwm: mtk-disp: Implement atomic API .get_state()") Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> --- drivers/pwm/pwm-mtk-disp.c | 10 ++++++++++ 1 file changed, 10 insertions(+)