[PATCH] drm/i915/backlight: fix CPU mode backlight takeover on LPT

[PATCH] drm/i915/backlight: fix CPU mode backlight takeover on LPT

[Jani Nikula]

The pch_get_backlight(), lpt_get_backlight(), and lpt_set_backlight()
functions operate directly on the hardware registers. If inverting the
value is needed, using intel_panel_compute_brightness(), it should only
be done in the interface between hardware registers and
panel->backlight.level.

The CPU mode takeover code added in commit 5b1ec9ac7ab5
("drm/i915/backlight: Fix backlight takeover on LPT, v3.") reads the
hardware register and converts to panel->backlight.level correctly,
however the value written back should remain in the hardware register
"domain".

This hasn't been an issue, because GM45 machines are the only known
users of i915.invert_brightness and the brightness invert quirk, and
without one of them no conversion is made. It's likely nobody's ever hit
the problem.

Fixes: 5b1ec9ac7ab5 ("drm/i915/backlight: Fix backlight takeover on LPT, v3.")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: <stable@vger.kernel.org> # v5.1+
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
 drivers/gpu/drm/i915/display/intel_panel.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_panel.c b/drivers/gpu/drm/i915/display/intel_panel.c
index 67f81ae995c4..7a4239d1c241 100644
--- a/drivers/gpu/drm/i915/display/intel_panel.c
+++ b/drivers/gpu/drm/i915/display/intel_panel.c
@@ -1649,16 +1649,13 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
 		val = pch_get_backlight(connector);
 	else
 		val = lpt_get_backlight(connector);
-	val = intel_panel_compute_brightness(connector, val);
-	panel->backlight.level = clamp(val, panel->backlight.min,
-				       panel->backlight.max);
 
 	if (cpu_mode) {
 		drm_dbg_kms(&dev_priv->drm,
 			    "CPU backlight register was enabled, switching to PCH override\n");
 
 		/* Write converted CPU PWM value to PCH override register */
-		lpt_set_backlight(connector->base.state, panel->backlight.level);
+		lpt_set_backlight(connector->base.state, val);
 		intel_de_write(dev_priv, BLC_PWM_PCH_CTL1,
 			       pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);
 
@@ -1666,6 +1663,10 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
 			       cpu_ctl2 & ~BLM_PWM_ENABLE);
 	}
 
+	val = intel_panel_compute_brightness(connector, val);
+	panel->backlight.level = clamp(val, panel->backlight.min,
+				       panel->backlight.max);
+
 	return 0;
 }
 
-- 
2.20.1

Re: [PATCH] drm/i915/backlight: fix CPU mode backlight takeover on LPT

[Lyude Paul]

Reviewed-by: Lyude Paul <lyude@redhat.com>

Let me know when you've pushed this upstream and I'll go ahead and send out a
rebased version of my backlight series.

On Fri, 2021-01-08 at 17:28 +0200, Jani Nikula wrote:
> The pch_get_backlight(), lpt_get_backlight(), and lpt_set_backlight()
> functions operate directly on the hardware registers. If inverting the
> value is needed, using intel_panel_compute_brightness(), it should only
> be done in the interface between hardware registers and
> panel->backlight.level.
> 
> The CPU mode takeover code added in commit 5b1ec9ac7ab5
> ("drm/i915/backlight: Fix backlight takeover on LPT, v3.") reads the
> hardware register and converts to panel->backlight.level correctly,
> however the value written back should remain in the hardware register
> "domain".
> 
> This hasn't been an issue, because GM45 machines are the only known
> users of i915.invert_brightness and the brightness invert quirk, and
> without one of them no conversion is made. It's likely nobody's ever hit
> the problem.
> 
> Fixes: 5b1ec9ac7ab5 ("drm/i915/backlight: Fix backlight takeover on LPT, v3.")
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: <stable@vger.kernel.org> # v5.1+
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_panel.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_panel.c
> b/drivers/gpu/drm/i915/display/intel_panel.c
> index 67f81ae995c4..7a4239d1c241 100644
> --- a/drivers/gpu/drm/i915/display/intel_panel.c
> +++ b/drivers/gpu/drm/i915/display/intel_panel.c
> @@ -1649,16 +1649,13 @@ static int lpt_setup_backlight(struct intel_connector
> *connector, enum pipe unus
>                 val = pch_get_backlight(connector);
>         else
>                 val = lpt_get_backlight(connector);
> -       val = intel_panel_compute_brightness(connector, val);
> -       panel->backlight.level = clamp(val, panel->backlight.min,
> -                                      panel->backlight.max);
>  
>         if (cpu_mode) {
>                 drm_dbg_kms(&dev_priv->drm,
>                             "CPU backlight register was enabled, switching to
> PCH override\n");
>  
>                 /* Write converted CPU PWM value to PCH override register */
> -               lpt_set_backlight(connector->base.state, panel-
> >backlight.level);
> +               lpt_set_backlight(connector->base.state, val);
>                 intel_de_write(dev_priv, BLC_PWM_PCH_CTL1,
>                                pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);
>  
> @@ -1666,6 +1663,10 @@ static int lpt_setup_backlight(struct intel_connector
> *connector, enum pipe unus
>                                cpu_ctl2 & ~BLM_PWM_ENABLE);
>         }
>  
> +       val = intel_panel_compute_brightness(connector, val);
> +       panel->backlight.level = clamp(val, panel->backlight.min,
> +                                      panel->backlight.max);
> +
>         return 0;
>  }
>  

-- 
Sincerely,
   Lyude Paul (she/her)
   Software Engineer at Red Hat
   
Note: I deal with a lot of emails and have a lot of bugs on my plate. If you've
asked me a question, are waiting for a review/merge on a patch, etc. and I
haven't responded in a while, please feel free to send me another email to check
on my status. I don't bite!

Re: [PATCH] drm/i915/backlight: fix CPU mode backlight takeover on LPT

[Jani Nikula]

On Fri, 08 Jan 2021, Lyude Paul <lyude@redhat.com> wrote:
> Reviewed-by: Lyude Paul <lyude@redhat.com>
>
> Let me know when you've pushed this upstream and I'll go ahead and send out a
> rebased version of my backlight series.

Pushed, thanks for the review.

I'm hoping to do more review of the series today, so please hold off on
actually sending the rebased version for a bit longer.

BR,
Jani.


>
> On Fri, 2021-01-08 at 17:28 +0200, Jani Nikula wrote:
>> The pch_get_backlight(), lpt_get_backlight(), and lpt_set_backlight()
>> functions operate directly on the hardware registers. If inverting the
>> value is needed, using intel_panel_compute_brightness(), it should only
>> be done in the interface between hardware registers and
>> panel->backlight.level.
>> 
>> The CPU mode takeover code added in commit 5b1ec9ac7ab5
>> ("drm/i915/backlight: Fix backlight takeover on LPT, v3.") reads the
>> hardware register and converts to panel->backlight.level correctly,
>> however the value written back should remain in the hardware register
>> "domain".
>> 
>> This hasn't been an issue, because GM45 machines are the only known
>> users of i915.invert_brightness and the brightness invert quirk, and
>> without one of them no conversion is made. It's likely nobody's ever hit
>> the problem.
>> 
>> Fixes: 5b1ec9ac7ab5 ("drm/i915/backlight: Fix backlight takeover on LPT, v3.")
>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Lyude Paul <lyude@redhat.com>
>> Cc: <stable@vger.kernel.org> # v5.1+
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  drivers/gpu/drm/i915/display/intel_panel.c | 9 +++++----
>>  1 file changed, 5 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_panel.c
>> b/drivers/gpu/drm/i915/display/intel_panel.c
>> index 67f81ae995c4..7a4239d1c241 100644
>> --- a/drivers/gpu/drm/i915/display/intel_panel.c
>> +++ b/drivers/gpu/drm/i915/display/intel_panel.c
>> @@ -1649,16 +1649,13 @@ static int lpt_setup_backlight(struct intel_connector
>> *connector, enum pipe unus
>>                 val = pch_get_backlight(connector);
>>         else
>>                 val = lpt_get_backlight(connector);
>> -       val = intel_panel_compute_brightness(connector, val);
>> -       panel->backlight.level = clamp(val, panel->backlight.min,
>> -                                      panel->backlight.max);
>>  
>>         if (cpu_mode) {
>>                 drm_dbg_kms(&dev_priv->drm,
>>                             "CPU backlight register was enabled, switching to
>> PCH override\n");
>>  
>>                 /* Write converted CPU PWM value to PCH override register */
>> -               lpt_set_backlight(connector->base.state, panel-
>> >backlight.level);
>> +               lpt_set_backlight(connector->base.state, val);
>>                 intel_de_write(dev_priv, BLC_PWM_PCH_CTL1,
>>                                pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);
>>  
>> @@ -1666,6 +1663,10 @@ static int lpt_setup_backlight(struct intel_connector
>> *connector, enum pipe unus
>>                                cpu_ctl2 & ~BLM_PWM_ENABLE);
>>         }
>>  
>> +       val = intel_panel_compute_brightness(connector, val);
>> +       panel->backlight.level = clamp(val, panel->backlight.min,
>> +                                      panel->backlight.max);
>> +
>>         return 0;
>>  }
>>  

-- 
Jani Nikula, Intel Open Source Graphics Center

Re: [PATCH] drm/i915/backlight: fix CPU mode backlight takeover on LPT

[Jani Nikula]

On Mon, 11 Jan 2021, Jani Nikula <jani.nikula@intel.com> wrote:
> On Fri, 08 Jan 2021, Lyude Paul <lyude@redhat.com> wrote:
>> Reviewed-by: Lyude Paul <lyude@redhat.com>
>>
>> Let me know when you've pushed this upstream and I'll go ahead and send out a
>> rebased version of my backlight series.
>
> Pushed, thanks for the review.
>
> I'm hoping to do more review of the series today, so please hold off on
> actually sending the rebased version for a bit longer.

Done, go ahead!

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center