Re: [PATCH v10 1/3] drm/i915: Add heuristic to determine better way to adjust brightness

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On Fri, 2017-06-02 at 17:42 +0000, Pandiyan, Dhinakaran wrote:

Somehow the CC's got removed in my previous reply, adding them back. See
one additional comment below.


> On Fri, 2017-05-26 at 18:42 -0700, Puthikorn Voravootivat wrote:
> > Add heuristic to decide that AUX or PWM pin should use for
> > backlight brightness adjustment and modify i915 param description
> > to have auto, force disable, and force enable.
> > 
> > The heuristic to determine that using AUX pin is better than using
> > PWM pin is that the panel support any of the feature list here.
> > - Regional backlight brightness adjustment
> > - Backlight PWM frequency set
> > - More than 8 bits resolution of brightness level
> > - Backlight enablement via AUX and not by BL_ENABLE pin
> > 
> > Signed-off-by: Puthikorn Voravootivat <puthik@xxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/i915/i915_params.c            |  7 +--
> >  drivers/gpu/drm/i915/i915_params.h            |  2 +-
> >  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 64 +++++++++++++++++++++++++--
> >  3 files changed, 66 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> > index b6a7e363d076..3758ae1f11b4 100644
> > --- a/drivers/gpu/drm/i915/i915_params.c
> > +++ b/drivers/gpu/drm/i915/i915_params.c
> > @@ -63,7 +63,7 @@ struct i915_params i915 __read_mostly = {
> >  	.huc_firmware_path = NULL,
> >  	.enable_dp_mst = true,
> >  	.inject_load_failure = 0,
> > -	.enable_dpcd_backlight = false,
> > +	.enable_dpcd_backlight = -1,
> >  	.enable_gvt = false,
> >  };
> >  
> > @@ -246,9 +246,10 @@ MODULE_PARM_DESC(enable_dp_mst,
> >  module_param_named_unsafe(inject_load_failure, i915.inject_load_failure, uint, 0400);
> >  MODULE_PARM_DESC(inject_load_failure,
> >  	"Force an error after a number of failure check points (0:disabled (default), N:force failure at the Nth failure check point)");
> > -module_param_named(enable_dpcd_backlight, i915.enable_dpcd_backlight, bool, 0600);
> > +module_param_named_unsafe(enable_dpcd_backlight, i915.enable_dpcd_backlight, int, 0600);
> >  MODULE_PARM_DESC(enable_dpcd_backlight,
> > -	"Enable support for DPCD backlight control (default:false)");
> > +	"Enable support for DPCD backlight control "
> > +	"(-1:auto (default), 0:force disable, 1:force enabled if supported");
> >  
> >  module_param_named(enable_gvt, i915.enable_gvt, bool, 0400);
> >  MODULE_PARM_DESC(enable_gvt,
> > diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> > index 34148cc8637c..ac02efce6e22 100644
> > --- a/drivers/gpu/drm/i915/i915_params.h
> > +++ b/drivers/gpu/drm/i915/i915_params.h
> > @@ -66,7 +66,7 @@
> >  	func(bool, verbose_state_checks); \
> >  	func(bool, nuclear_pageflip); \
> >  	func(bool, enable_dp_mst); \
> > -	func(bool, enable_dpcd_backlight); \
> > +	func(int, enable_dpcd_backlight); \


Please move this above the bools, see comment in code that's a few lines
above.

-DK

> >  	func(bool, enable_gvt)
> >  
> >  #define MEMBER(T, member) T member
> > diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > index a0995c00fc84..c89aae804659 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > @@ -43,6 +43,9 @@ static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
> >  	else
> >  		reg_val &= ~(DP_EDP_BACKLIGHT_ENABLE);
> >  
> > +	/* TODO: If the panel also support enabling backlight via BL_ENABLE pin,
> > +	 * the backlight will be enabled again in _intel_edp_backlight_on()
> > +	 */
> 
> Unrelated hunk, please remove. This should have been included in one of
> the previous patches.
> 
> >  	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
> >  			       reg_val) != 1) {
> >  		DRM_DEBUG_KMS("Failed to %s aux backlight\n",
> > @@ -168,15 +171,66 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector)
> >  	/* Check the  eDP Display control capabilities registers to determine if
> >  	 * the panel can support backlight control over the aux channel
> >  	 */
> > -	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
> > -	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
> > -	    !(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP)) {
> > +	if ((intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> > +	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
> >  		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
> >  		return true;
> >  	}
> >  	return false;
> >  }
> >  
> > +/*
> > + * Heuristic function whether we should use AUX for backlight adjustment or not.
> > + *
> > + * We should use AUX for backlight brightness adjustment if panel doesn't this
> > + * via PWM pin or using AUX is better than using PWM pin.
> > + *
> > + * The heuristic to determine that using AUX pin is better than using PWM pin is
> > + * that the panel support any of the feature list here.
> > + * - Regional backlight brightness adjustment
> > + * - Backlight PWM frequency set
> > + * - More than 8 bits resolution of brightness level
> > + * - Backlight enablement via AUX and not by BL_ENABLE pin
> > + *
> > + * If all above are not true, assume that using PWM pin is better.
> > + */
> > +static bool
> > +intel_dp_aux_display_control_heuristic(struct intel_connector *connector)
> > +{
> > +	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
> > +	uint8_t reg_val;
> > +
> > +	/* Panel doesn't support adjusting backlight brightness via PWN pin */
> > +	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))
> 
> Isn't BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP in edp_dpcd[2] ?
> 
> 
> > +		return true;
> > +
> > +	/* Panel supports regional backlight brightness adjustment */
> > +	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_GENERAL_CAP_3,
> 
> Spec says this register is new to eDP 1.4. I don't see a check for
> version.
> 
>  
> > +			      &reg_val) != 1) {
> > +		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
> > +			       DP_EDP_GENERAL_CAP_3);
> > +		return false;
> > +	}
> > +	if (reg_val > 0)
> > +		return true;
> > +
> > +	/* Panel supports backlight PWM frequency set */
> > +	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> > +		return true;
> > +
> > +	/* Panel supports more than 8 bits resolution of brightness level */
> > +	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> > +		return true;
> 
> I don't know if more than 8 bits is relatively better than the
> resolution PWM pin allows. I guess, we could fix that later by comparing
> the number of brightness levels.
> 
> > +
> > +	/* Panel supports enabling backlight via AUX but not by BL_ENABLE pin */
> > +	if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> > +	    !(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP))
> > +		return true;
> > +
> > +	return false;
> > +
> > +}
> > +
> >  int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
> >  {
> >  	struct intel_panel *panel = &intel_connector->panel;
> > @@ -187,6 +241,10 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
> >  	if (!intel_dp_aux_display_control_capable(intel_connector))
> >  		return -ENODEV;
> >  
> > +	if (i915.enable_dpcd_backlight == -1 &&
> > +	    !intel_dp_aux_display_control_heuristic(intel_connector))
> > +		return -ENODEV;
> > +
> >  	panel->backlight.setup = intel_dp_aux_setup_backlight;
> >  	panel->backlight.enable = intel_dp_aux_enable_backlight;
> >  	panel->backlight.disable = intel_dp_aux_disable_backlight;
> 
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