[PATCH v2 15/17] drm/dp: Add a quirk for a DELL P2715Q MST payload allocation problem

[Imre Deak]

The DELL P2715Q monitor's MST hub has a payload allocation problem,
where the VCPI used to reserve the last two time slots (at position
0x3e, 0x3f) in the hub's payload table, this VCPI can't be reused for
later payload configurations. To work around the problem in a follow-up
patch the driver needs to reset the payload table after all payloads
have been freed; add a quirk the driver can use to detect the monitor
and apply the WA if needed.

Cc: Lyude Paul <lyude at redhat.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: dri-devel at lists.freedesktop.org
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/display/drm_dp_helper.c | 2 ++
 include/drm/display/drm_dp_helper.h     | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index 16565a0a5da6d..e2cf4b4fe11ea 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -2244,6 +2244,8 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
 	{ OUI(0x90, 0xCC, 0x24), DEVICE_ID_ANY, true, BIT(DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) },
 	/* 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) },
+	/* DELL P2715Q MST payload table must be reset after the two last payload slots get allocated. */
+	{ OUI(0x00, 0xe0, 0x4c), DEVICE_ID('D', 'p', '1', '.', '2', 0), true, BIT(DP_DPCD_QUIRK_MST_PAYLOAD_TABLE_RESET_WA) },
 };
 
 #undef OUI
diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
index ab55453f2d2cd..fcd445921ec9d 100644
--- a/include/drm/display/drm_dp_helper.h
+++ b/include/drm/display/drm_dp_helper.h
@@ -620,6 +620,14 @@ enum drm_dp_quirk {
 	 * the DP_MAX_LINK_RATE register reporting a lower max multiplier.
 	 */
 	DP_DPCD_QUIRK_CAN_DO_MAX_LINK_RATE_3_24_GBPS,
+	/**
+	 * @DP_DPCD_QUIRK_MST_PAYLOAD_TABLE_RESET_WA:
+	 *
+	 * An bug in the MST branch device's payload allocation logic requires
+	 * the payload table to be reset after its last two payload slots get
+	 * allocated.
+	 */
+	DP_DPCD_QUIRK_MST_PAYLOAD_TABLE_RESET_WA,
 };
 
 /**
-- 
2.37.1