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,
®_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,
> - ®_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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