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

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May be the older panel might not work well with this feature.
David/Jani, what do you think about adding check that the panel is eDP
1.4 or later in the heuristic?

diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
index b25cd88fc1c5..e63f2296fd34 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -292,7 +292,7 @@ intel_dp_aux_display_control_capable(struct
intel_connector *connector)
  * 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.
+ * that the panel is eDP 1.4 or later and support any of the feature list here.
  * - Regional backlight brightness adjustment
  * - Backlight PWM frequency set
  * - More than 8 bits resolution of brightness level
@@ -310,6 +310,10 @@ intel_dp_aux_display_control_heuristic(struct
intel_connector *connector)
        if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))
                return true;

+       /* Enable this for eDP 1.4 panel or later. */
+       if (intel_dp->edp_dpcd[0] < DP_EDP_14)
+               return false;
+
        /* Panel supports regional backlight brightness adjustment */
        if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_GENERAL_CAP_3,
                              &reg_val) != 1) {

On Mon, Jul 10, 2017 at 7:23 AM, David Weinehall
<david.weinehall@xxxxxxxxxxxxxxx> wrote:
> This reverts commit 560a758d39c616f83ac25ff6e0816a49ebe6401c.
>
> This patch has been identified to introduce a backlight regression
> on at least two different platforms; either the heuristic is broken
> (if so the patch needs to be reworked) or the in-kernel DPCD backlight
> support is broken (if so it's premature to enable DPCD backlight
> even if the platforms support it).
>
> Signed-off-by: David Weinehall <david.weinehall@xxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/i915/i915_params.c            |  7 ++-
>  drivers/gpu/drm/i915/i915_params.h            |  1 -
>  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 61 ++-------------------------
>  3 files changed, 6 insertions(+), 63 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 88b9d3e6713a..bec5ade371b0 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,
>         .enable_dbc = true,
>  };
> @@ -247,10 +247,9 @@ 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 057e203e6bda..6a88c76664db 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); \
> diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> index b25cd88fc1c5..f32dec02e540 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -277,66 +277,15 @@ 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;
> @@ -347,10 +296,6 @@ 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;
> --
> 2.13.2
>
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