From: Ville Syrjälä ville.syrjala@linux.intel.com

According to the DP spec TPS4 is mandatory for HBR3. We have however seen some broken eDP sinks that violate this and declare support for HBR3 without TPS4 support.

At least in the case of the icl Dell XPS 13 7390 this results in an unstable output.

Reject HBR3 when TPS4 supports is unavailable on the sink.

Cc: stable@vger.kernel.org Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/5969 Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com --- drivers/gpu/drm/i915/display/intel_dp.c | 36 ++++++++++++++++++++----- 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c index 205ec315b413..61a58ff801a5 100644 --- a/drivers/gpu/drm/i915/display/intel_dp.c +++ b/drivers/gpu/drm/i915/display/intel_dp.c @@ -172,10 +172,22 @@ int intel_dp_link_symbol_clock(int rate)

static int max_dprx_rate(struct intel_dp *intel_dp) { + int max_rate; + if (intel_dp_tunnel_bw_alloc_is_enabled(intel_dp)) - return drm_dp_tunnel_max_dprx_rate(intel_dp->tunnel); + max_rate = drm_dp_tunnel_max_dprx_rate(intel_dp->tunnel); + else + 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. + */ + if (!drm_dp_tps4_supported(intel_dp->dpcd)) + max_rate = min(max_rate, 540000);

- return drm_dp_bw_code_to_link_rate(intel_dp->dpcd[DP_MAX_LINK_RATE]); + return max_rate; }

static int max_dprx_lane_count(struct intel_dp *intel_dp) @@ -4180,10 +4192,7 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp) sink_rates, sizeof(sink_rates));

for (i = 0; i < ARRAY_SIZE(sink_rates); i++) { - int val = le16_to_cpu(sink_rates[i]); - - if (val == 0) - break; + int rate;

/* Value read multiplied by 200kHz gives the per-lane * link rate in kHz. The source rates are, however, @@ -4191,7 +4200,20 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp) * back to symbols is * (val * 200kHz)*(8/10 ch. encoding)*(1/8 bit to Byte) */ - intel_dp->sink_rates[i] = (val * 200) / 10; + rate = le16_to_cpu(sink_rates[i]) * 200 / 10; + + 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. + */ + if (rate >= 810000 && !drm_dp_tps4_supported(intel_dp->dpcd)) + break; + + intel_dp->sink_rates[i] = rate; } intel_dp->num_sink_rates = i; }