[Intel-gfx] [PATCH RESEND v4 1/6] drm/i915: Add DPCD preferred mode for backlight control

[Pandiyan, Dhinakaran]

Sorry for the wait. This is not a complete review, just some quick
comments for now.


On Tue, 2017-04-18 at 16:48 -0700, Puthikorn Voravootivat wrote:
> Currently the intel_dp_aux_backlight driver requires eDP panel
> to not also support backlight adjustment via PWM pin to use
> this driver.
> 
> This force the eDP panel that support both ways of backlight
> adjustment to do it via PWM pin.
> 
> This patch adds the new prefer DPCD mode in the i915_param
> to make it enable to prefer DPCD over the PWM via kernel param.
> 
> This patch also add a check to DP_EDP_BACKLIGHT_AUX_ENABLE_CAP
> in set_aux_backlight_enable() since the backlight enablement
> can be done via BL_ENABLE eDP connector pin in the case that
> it does not support doing that via AUX.
> 
> Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
> ---
>  drivers/gpu/drm/i915/i915_params.c            |  6 ++---
>  drivers/gpu/drm/i915/i915_params.h            |  2 +-
>  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 33 +++++++++++++++++++--------
>  3 files changed, 27 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index b6a7e363d076..960393dd5edf 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 = 0,
>  	.enable_gvt = false,
>  };
>  
> @@ -246,9 +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(enable_dpcd_backlight, i915.enable_dpcd_backlight, bool, 0600);
> +module_param_named(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 (0:disable (default), 1:prefer PWM pin, 2: prefer DPCD)");

I looked at other int parameters, -1=default, 0=disable(prefer PWM in
your case), 1=enable(prefer DPCD) seems like the more common way to do
this.


>  
>  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..bf6e2c60f697 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -51,6 +51,7 @@
>  	func(int, use_mmio_flip); \
>  	func(int, mmio_debug); \
>  	func(int, edp_vswing); \
> +	func(int, enable_dpcd_backlight); \
>  	func(unsigned int, inject_load_failure); \
>  	/* leave bools at the end to not create holes */ \
>  	func(bool, alpha_support); \
> @@ -66,7 +67,6 @@
>  	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 6532e226db29..42f73d9a3ccf 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -28,6 +28,10 @@ static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
>  {
>  	uint8_t reg_val = 0;
>  
> +	/* Early return when display use other mechanism to enable backlight. */
> +	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
> +		return;
> +
>  	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
>  			      &reg_val) < 0) {
>  		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
> @@ -138,27 +142,36 @@ static bool
>  intel_dp_aux_display_control_capable(struct intel_connector *connector)
>  {
>  	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
> +	bool supported;
>  
>  	/* 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[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> -	    !((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) ||
> -	      (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))) {
> -		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
> -		return true;
> +	switch (i915.enable_dpcd_backlight) {
> +	case 1: /* prefer PWM pin */
> +		supported = (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> +			    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> +			    !(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) &&
> +			    !(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP);
> +		break;
> +	case 2: /* prefer DPCD */
> +		supported = (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> +			    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
> +		break;
> +	default:
> +		supported = false;
>  	}
> -	return false;
> +
> +	if (supported)
> +		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
> +
> +	return supported;


If i915.enable_dpcd_backlight = 0, aren't you returning an uninitialized
variable here?

-DK


>  }
>  
>  int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
>  {
>  	struct intel_panel *panel = &intel_connector->panel;
>  
> -	if (!i915.enable_dpcd_backlight)
> -		return -ENODEV;
> -
>  	if (!intel_dp_aux_display_control_capable(intel_connector))
>  		return -ENODEV;
>