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

["Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>]

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@chromium.org>
> ---
>  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); \
>  	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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