Re: [PATCH 2/2] Revert "drm/i915: Add heuristic to determine better way to adjust brightness"

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 20 Jul 2017, "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com> wrote:
> On Thu, 2017-07-20 at 12:25 +0300, Jani Nikula wrote:
>> This reverts commit 560a758d39c616f83ac25ff6e0816a49ebe6401c.
>> 
>> The DPCD backlight commits regress a Thinkpad X1 Carbon 4th Gen and a
>> BXT-P (in CI). Enabling dynamic backlight boots to a black screen, and
>> enabling DPCD backlight leads to a black screen after suspend/resume.
>> 
>
>
> Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com> for
> both patches.

Thanks for the review, both pushed, with Daniel's IRC ack on top.

BR,
Jani.

>
>> References: http://mid.mail-archive.com/20170706135349.6tu3lz7uehazlnnn@boom
>> References: http://mid.mail-archive.com/20170627132326.f2q3yn4bh5flji4q@boom
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101619
>> Reported-by: David Weinehall <david.weinehall@linux.intel.com>
>> Fixes: 560a758d39c6 ("drm/i915: Add heuristic to determine better way to adjust brightness")
>> Cc: Jenny TC <jenny.tc@intel.com>
>> Cc: David Weinehall <david.weinehall@linux.intel.com>
>> Cc: Puthikorn Voravootivat <puthik@chromium.org>
>> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Cc: intel-gfx@lists.freedesktop.org
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  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 | 61 ++-------------------------
>>  3 files changed, 7 insertions(+), 63 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
>> index 5b5ab15d191f..14e2c2e57f96 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 = -1,
>> +	.enable_dpcd_backlight = false,
>>  	.enable_gvt = false,
>>  };
>>  
>> @@ -246,10 +246,9 @@ 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_unsafe(enable_dpcd_backlight, i915.enable_dpcd_backlight, int, 0600);
>> +module_param_named(enable_dpcd_backlight, i915.enable_dpcd_backlight, bool, 0600);
>>  MODULE_PARM_DESC(enable_dpcd_backlight,
>> -	"Enable support for DPCD backlight control "
>> -	"(-1:auto (default), 0:force disable, 1:force enabled if supported");
>> +	"Enable support for DPCD backlight control (default:false)");
>>  
>>  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 0d6cf9138dc4..febbfdbd30bd 100644
>> --- a/drivers/gpu/drm/i915/i915_params.h
>> +++ b/drivers/gpu/drm/i915/i915_params.h
>> @@ -53,7 +53,6 @@
>>  	func(int, edp_vswing); \
>>  	func(int, reset); \
>>  	func(unsigned int, inject_load_failure); \
>> -	func(int, enable_dpcd_backlight); \
>>  	/* leave bools at the end to not create holes */ \
>>  	func(bool, alpha_support); \
>>  	func(bool, enable_cmd_parser); \
>> @@ -67,6 +66,7 @@
>>  	func(bool, verbose_state_checks); \
>>  	func(bool, nuclear_pageflip); \
>>  	func(bool, enable_dp_mst); \
>> +	func(bool, 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 fea161727c6e..d2830ba3162e 100644
>> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
>> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
>> @@ -251,66 +251,15 @@ 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)) {
>> +	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)) {
>>  		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[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))
>> -		return true;
>> -
>> -	/* Panel supports regional backlight brightness adjustment */
>> -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_GENERAL_CAP_3,
>> -			      &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;
>> -
>> -	/* 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;
>> @@ -321,10 +270,6 @@ 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;

-- 
Jani Nikula, Intel Open Source Technology Center
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