The Synaptics MST hubs expose some sink EDID modes with a reduced HBLANK
period, presumedly to save BW, which the hub expands before forwarding
the stream to the sink. In particular a 4k mode with a standard CVT
HBLANK period is exposed with either a CVT reduced blank RBv1 (80 pixel)
or a non-CVT 56 pixel HBLANK period. The DP standard describes the above
HBLANK expansion functionality, but it requires enabling this explicitly,
whereas these hubs apply the expansion transparently.
Such modes will work okay until DSC decompression is enabled in the hub
for the given sink, but after this the same mode will not work reliably
in decompressed mode. As a workaround force enable DSC for such modes.
OTOH DSC for these modes will only work above a certain compressed bpp
threshold which depends on the link rate, so apply this limit as well
in the workaround.
Apply the workaround only for Synaptics hubs which support the HBLANK
expansion.
Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
---
.../drm/i915/display/intel_display_types.h | 2 +
drivers/gpu/drm/i915/display/intel_dp_mst.c | 109 +++++++++++++++++-
2 files changed, 107 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 65ea37fe8cff3..409dbf8a2a1cd 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -624,6 +624,8 @@ struct intel_connector {
struct drm_dp_aux *dsc_decompression_aux;
u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE];
u8 fec_capability;
+
+ u8 dsc_hblank_expansion_quirk:1;
} dp;
/* Work struct to schedule a uevent on link train failure */
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index a1ea75cd5ea84..9124e9cdf4c79 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -345,8 +345,69 @@ static int intel_dp_mst_update_slots(struct intel_encoder *encoder,
return 0;
}
+static bool
+hblank_expansion_quirk_needs_dsc(const struct intel_connector *connector,
+ const struct intel_crtc_state *crtc_state)
+{
+ const struct drm_display_mode *adjusted_mode =
+ &crtc_state->hw.adjusted_mode;
+
+ if (!connector->dp.dsc_hblank_expansion_quirk)
+ return false;
+
+ if (adjusted_mode->htotal - adjusted_mode->hdisplay > 80)
+ return false;
+
+ return true;
+}
+
+static bool
+adjust_limits_for_dsc_hblank_expansion_quirk(const struct intel_connector *connector,
+ const struct intel_crtc_state *crtc_state,
+ struct link_config_limits *limits,
+ bool dsc)
+{
+ struct drm_i915_private *i915 = to_i915(connector->base.dev);
+ const struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+ int min_bpp_x16 = limits->link.min_bpp_x16;
+
+ if (!hblank_expansion_quirk_needs_dsc(connector, crtc_state))
+ return true;
+
+ if (!dsc) {
+ drm_dbg_kms(&i915->drm,
+ "[CRTC:%d:%s][CONNECTOR:%d:%s] DSC required by hblank expansion quirk\n",
+ crtc->base.base.id, crtc->base.name,
+ connector->base.base.id, connector->base.name);
+ return false;
+ }
+
+ drm_WARN_ON(&i915->drm, limits->min_rate != limits->max_rate);
+
+ if (limits->max_rate < 540000)
+ min_bpp_x16 = to_bpp_x16(13);
+ else if (limits->max_rate < 810000)
+ min_bpp_x16 = to_bpp_x16(10);
+
+ if (limits->link.min_bpp_x16 < min_bpp_x16) {
+ drm_dbg_kms(&i915->drm,
+ "[CRTC:%d:%s][CONNECTOR:%d:%s] Increasing link min bpp to " BPP_X16_FMT " due to hblank expansion quirk\n",
+ crtc->base.base.id, crtc->base.name,
+ connector->base.base.id, connector->base.name,
+ BPP_X16_ARGS(min_bpp_x16));
+
+ if (limits->link.max_bpp_x16 < min_bpp_x16)
+ return false;
+
+ limits->link.min_bpp_x16 = min_bpp_x16;
+ }
+
+ return true;
+}
+
static bool
intel_dp_mst_compute_config_limits(struct intel_dp *intel_dp,
+ const struct intel_connector *connector,
struct intel_crtc_state *crtc_state,
bool dsc,
struct link_config_limits *limits)
@@ -374,10 +435,16 @@ intel_dp_mst_compute_config_limits(struct intel_dp *intel_dp,
intel_dp_adjust_compliance_config(intel_dp, crtc_state, limits);
- return intel_dp_compute_config_link_bpp_limits(intel_dp,
- crtc_state,
- dsc,
- limits);
+ if (!intel_dp_compute_config_link_bpp_limits(intel_dp,
+ crtc_state,
+ dsc,
+ limits))
+ return false;
+
+ return adjust_limits_for_dsc_hblank_expansion_quirk(connector,
+ crtc_state,
+ limits,
+ dsc);
}
static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
@@ -404,6 +471,7 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
dsc_needed = intel_dp->force_dsc_en ||
!intel_dp_mst_compute_config_limits(intel_dp,
+ connector,
pipe_config,
false,
&limits);
@@ -426,6 +494,7 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
str_yes_no(intel_dp->force_dsc_en));
if (!intel_dp_mst_compute_config_limits(intel_dp,
+ connector,
pipe_config,
true,
&limits))
@@ -1205,6 +1274,36 @@ intel_dp_mst_read_decompression_port_dsc_caps(struct intel_dp *intel_dp,
intel_dp_get_dsc_sink_cap(dpcd_caps[DP_DPCD_REV], connector);
}
+static bool detect_dsc_hblank_expansion_quirk(const struct intel_connector *connector)
+{
+ struct drm_i915_private *i915 = to_i915(connector->base.dev);
+ struct drm_dp_desc desc;
+ u8 dpcd[DP_RECEIVER_CAP_SIZE];
+
+ if (!connector->dp.dsc_decompression_aux)
+ return false;
+
+ if (drm_dp_read_desc(connector->dp.dsc_decompression_aux,
+ &desc, true) < 0)
+ return false;
+
+ if (!drm_dp_has_quirk(&desc,
+ DP_DPCD_QUIRK_HBLANK_EXPANSION_REQUIRES_DSC))
+ return false;
+
+ if (drm_dp_read_dpcd_caps(connector->dp.dsc_decompression_aux, dpcd) < 0)
+ return false;
+
+ if (!(dpcd[DP_RECEIVE_PORT_0_CAP_0] & DP_HBLANK_EXPANSION_CAPABLE))
+ return false;
+
+ drm_dbg_kms(&i915->drm,
+ "[CONNECTOR:%d:%s] DSC HBLANK expansion quirk detected\n",
+ connector->base.base.id, connector->base.name);
+
+ return true;
+}
+
static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
struct drm_dp_mst_port *port,
const char *pathprop)
@@ -1245,6 +1344,8 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
*/
intel_connector->dp.dsc_decompression_aux = &intel_dp->aux;
intel_dp_mst_read_decompression_port_dsc_caps(intel_dp, intel_connector);
+ intel_connector->dp.dsc_hblank_expansion_quirk =
+ detect_dsc_hblank_expansion_quirk(intel_connector);
for_each_pipe(dev_priv, pipe) {
struct drm_encoder *enc =
--
2.39.2
