Re: [PATCH] drm/i915/dp: Allow HBR3 without TPS4 support for eDP panels

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

On Tue, 20 May 2025, Ankit Nautiyal <ankit.k.nautiyal@intel.com> wrote:
> Commit 584cf613c24a ("drm/i915/dp: Reject HBR3 when sink doesn't support
> TPS4") introduced a blanket rejection of HBR3 link rate when the sink does
> not support TPS4. While this was intended to address instability observed
> on certain eDP panels [1], the TPS4 requirement is only mandated for DPRX
> and not for eDPRX.
>
> This change inadvertently causes blank screens on some eDP panels that do
> not advertise TPS4 support, and require HBR3 to operate at their fixed
> native resolution.
>
> To restore functionality for such panels do not reject HBR3 when sink
> doesn't support TPS4. Instead reject HBR3 for specific panel that are
> not able to handle HBR3 [1].
>
> [1] https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/5969
>
> Fixes: 584cf613c24a ("drm/i915/dp: Reject HBR3 when sink doesn't support TPS4")
> Cc: stable@vger.kernel.org
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/display/drm_dp_helper.c |  2 ++
>  drivers/gpu/drm/i915/display/intel_dp.c | 21 ++++++++++-----------
>  include/drm/display/drm_dp_helper.h     |  7 +++++++
>  3 files changed, 19 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> index f2a6559a2710..bf66489c9202 100644
> --- a/drivers/gpu/drm/display/drm_dp_helper.c
> +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> @@ -2526,6 +2526,8 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
>  	{ OUI(0x00, 0x0C, 0xE7), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_HBLANK_EXPANSION_REQUIRES_DSC) },
>  	/* Apple MacBookPro 2017 15 inch eDP Retina panel reports too low DP_MAX_LINK_RATE */
>  	{ OUI(0x00, 0x10, 0xfa), DEVICE_ID(101, 68, 21, 101, 98, 97), false, BIT(DP_DPCD_QUIRK_CAN_DO_MAX_LINK_RATE_3_24_GBPS) },
> +	/* Novatek panel */
> +	{ OUI(0x38, 0xEC, 0x11), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_HBR3) },
>  };
>  
>  #undef OUI
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 21297bc4cc00..0bfc84cbd50d 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -184,13 +184,13 @@ static int max_dprx_rate(struct intel_dp *intel_dp)
>  		max_rate = drm_dp_bw_code_to_link_rate(intel_dp->dpcd[DP_MAX_LINK_RATE]);
>  
>  	/*
> -	 * Some broken eDP sinks illegally declare support for
> -	 * HBR3 without TPS4, and are unable to produce a stable
> -	 * output. Reject HBR3 when TPS4 is not available.
> +	 * Some broken eDP sinks declare support for HBR3 but are unable to
> +	 * produce a stable output. For these panel reject HBR3.
>  	 */
> -	if (max_rate >= 810000 && !drm_dp_tps4_supported(intel_dp->dpcd)) {
> +	if (max_rate >= 810000 &&
> +	    drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_HBR3)) {

This does work, but I was thinking the quirk would be that the max is
HBR2. Same thing, but more generic? DP_DPCD_QUIRK_MAX_HBR2 maybe?

With that, you could drop the max_rate >= 810000 from here. (Though the
next check below does need the rate check as it stops the loop.)

>  		drm_dbg_kms(display->drm,
> -			    "[ENCODER:%d:%s] Rejecting HBR3 due to missing TPS4 support\n",
> +			    "[ENCODER:%d:%s] Rejecting HBR3 due to DP_DPCD_QUIRK_HBR3\n",
>  			    encoder->base.base.id, encoder->base.name);
>  		max_rate = 540000;
>  	}
> @@ -4296,15 +4296,14 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp)
>  
>  			if (rate == 0)
>  				break;
> -
>  			/*
> -			 * Some broken eDP sinks illegally declare support for
> -			 * HBR3 without TPS4, and are unable to produce a stable
> -			 * output. Reject HBR3 when TPS4 is not available.
> +			 * Some broken eDP sinks declare support for HBR3 but are unable to
> +			 * produce a stable output. For these panel reject HBR3.
>  			 */
> -			if (rate >= 810000 && !drm_dp_tps4_supported(intel_dp->dpcd)) {
> +			if (rate >= 810000 &&
> +			    drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_HBR3)) {
>  				drm_dbg_kms(display->drm,
> -					    "[ENCODER:%d:%s] Rejecting HBR3 due to missing TPS4 support\n",
> +					    "[ENCODER:%d:%s] Rejecting HBR3 due to DP_DPCD_QUIRK_HBR3\n",
>  					    encoder->base.base.id, encoder->base.name);
>  				break;
>  			}
> diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
> index e4ca35143ff9..5e60a37b61ce 100644
> --- a/include/drm/display/drm_dp_helper.h
> +++ b/include/drm/display/drm_dp_helper.h
> @@ -814,6 +814,13 @@ enum drm_dp_quirk {
>  	 * requires enabling DSC.
>  	 */
>  	DP_DPCD_QUIRK_HBLANK_EXPANSION_REQUIRES_DSC,
> +
> +	/**
> +	 * @DP_DPCD_QUIRK_HBR3:
> +	 *
> +	 * The device supports HBR3 but is unable to produce stable output.

I think DP_DPCD_QUIRK_MAX_HBR2 is easier to explain too.

What do you think?

BR,
Jani.



> +	 */
> +	DP_DPCD_QUIRK_HBR3,
>  };
>  
>  /**

-- 
Jani Nikula, Intel