linux-kernel - [PATCH 5.10 041/130] drm/amd/display: Allow DSC on supported MST branch devices

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Message-Id: <20211206145601.098660226@linuxfoundation.org>
Date:   Mon,  6 Dec 2021 15:55:58 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hersen Wu <hersenxs.wu@....com>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Daniel Wheeler <daniel.wheeler@....com>,
        Alex Deucher <alexander.deucher@....com>
Subject: [PATCH 5.10 041/130] drm/amd/display: Allow DSC on supported MST branch devices

From: Nicholas Kazlauskas <nicholas.kazlauskas@....com>

commit 94ebc035456a4ccacfbbef60c444079a256623ad upstream.

[Why]
When trying to lightup two 4k60 non-DSC displays behind a branch device
that supports DSC we can't lightup both at once due to bandwidth
limitations - each requires 48 VCPI slots but we only have 63.

[How]
The workaround already exists in the code but is guarded by a CONFIG
that cannot be set by the user and shouldn't need to be.

Check for specific branch device IDs to device whether to enable
the workaround for multiple display scenarios.

Reviewed-by: Hersen Wu <hersenxs.wu@....com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@....com>
Tested-by: Daniel Wheeler <daniel.wheeler@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Cc: stable@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c |   20 +++++++++---
 1 file changed, 16 insertions(+), 4 deletions(-)

--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -36,6 +36,8 @@
 #include "dm_helpers.h"
 
 #include "dc_link_ddc.h"
+#include "ddc_service_types.h"
+#include "dpcd_defs.h"
 
 #include "i2caux_interface.h"
 #if defined(CONFIG_DEBUG_FS)
@@ -152,6 +154,16 @@ static const struct drm_connector_funcs
 };
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
+static bool needs_dsc_aux_workaround(struct dc_link *link)
+{
+	if (link->dpcd_caps.branch_dev_id == DP_BRANCH_DEVICE_ID_90CC24 &&
+	    (link->dpcd_caps.dpcd_rev.raw == DPCD_REV_14 || link->dpcd_caps.dpcd_rev.raw == DPCD_REV_12) &&
+	    link->dpcd_caps.sink_count.bits.SINK_COUNT >= 2)
+		return true;
+
+	return false;
+}
+
 static bool validate_dsc_caps_on_connector(struct amdgpu_dm_connector *aconnector)
 {
 	struct dc_sink *dc_sink = aconnector->dc_sink;
@@ -159,7 +171,7 @@ static bool validate_dsc_caps_on_connect
 	u8 dsc_caps[16] = { 0 };
 
 	aconnector->dsc_aux = drm_dp_mst_dsc_aux_for_port(port);
-#if defined(CONFIG_HP_HOOK_WORKAROUND)
+
 	/*
 	 * drm_dp_mst_dsc_aux_for_port() will return NULL for certain configs
 	 * because it only check the dsc/fec caps of the "port variable" and not the dock
@@ -169,10 +181,10 @@ static bool validate_dsc_caps_on_connect
 	 * Workaround: explicitly check the use case above and use the mst dock's aux as dsc_aux
 	 *
 	 */
-
-	if (!aconnector->dsc_aux && !port->parent->port_parent)
+	if (!aconnector->dsc_aux && !port->parent->port_parent &&
+	    needs_dsc_aux_workaround(aconnector->dc_link))
 		aconnector->dsc_aux = &aconnector->mst_port->dm_dp_aux.aux;
-#endif
+
 	if (!aconnector->dsc_aux)
 		return false;