[PATCH v9 0/6] DSC MST support in DRM

[PATCH v9 0/6] DSC MST support in DRM

[David Francis]

Add necessary support for MST DSC.
(Display Stream Compression over Multi-Stream Transport)

Note that even though each of these patches has Reviewed-by,
this patchset is not ready for merge, because
a) The last two patches have been reviewed internally by
Wenjing Liu, but that review is only of their implementation
of DP policy, not their stylistic or architectural suitability
for the kernel
b) There is ongoing discussion of if any AMD MST DSC code
should be merged until AMD uses the DRM MST atomic framework

v4: Split patchset and rebase onto drm-tip
v5: Clean up formatting, make new quirk
v6: Fix typo, split last patch in two
v7: Fix compilation warnings
v8: Fix a missing mutex_unlock
v9: Refactor last patch

David Francis (6):
  drm/dp_mst: Add PBN calculation for DSC modes
  drm/dp_mst: Parse FEC capability on MST ports
  drm/dp_mst: Add MST support to DP DPCD R/W functions
  drm/dp_mst: Fill branch->num_ports
  drm/dp_mst: Add new quirk for Synaptics MST hubs
  drm/dp_mst: Add helpers for MST DSC and virtual DPCD aux

 .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c |   2 +-
 drivers/gpu/drm/drm_dp_aux_dev.c              |  12 +-
 drivers/gpu/drm/drm_dp_helper.c               |  32 +++-
 drivers/gpu/drm/drm_dp_mst_topology.c         | 173 +++++++++++++++++-
 drivers/gpu/drm/i915/display/intel_dp_mst.c   |   2 +-
 drivers/gpu/drm/nouveau/dispnv50/disp.c       |   2 +-
 drivers/gpu/drm/radeon/radeon_dp_mst.c        |   2 +-
 include/drm/drm_dp_helper.h                   |   7 +
 include/drm/drm_dp_mst_helper.h               |   8 +-
 9 files changed, 210 insertions(+), 30 deletions(-)

-- 
2.17.1

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[PATCH v9 1/6] drm/dp_mst: Add PBN calculation for DSC modes

[David Francis]

With DSC, bpp can be fractional in multiples of 1/16.

Change drm_dp_calc_pbn_mode to reflect this, adding a new
parameter bool dsc. When this parameter is true, treat the
bpp parameter as having units not of bits per pixel, but
1/16 of a bit per pixel

v2: Don't add separate function for this

Cc: amd-gfx@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Cc: intel-gfx@lists.freedesktop.org
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
---
 .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c    |  2 +-
 drivers/gpu/drm/drm_dp_mst_topology.c            | 16 ++++++++++++----
 drivers/gpu/drm/i915/display/intel_dp_mst.c      |  2 +-
 drivers/gpu/drm/nouveau/dispnv50/disp.c          |  2 +-
 drivers/gpu/drm/radeon/radeon_dp_mst.c           |  2 +-
 include/drm/drm_dp_mst_helper.h                  |  3 +--
 6 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
index a0ed0154a9f0..abafb5221b44 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
@@ -235,7 +235,7 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
 
 		/* TODO need to know link rate */
 
-		pbn = drm_dp_calc_pbn_mode(clock, bpp);
+		pbn = drm_dp_calc_pbn_mode(clock, bpp, false);
 
 		slots = drm_dp_find_vcpi_slots(mst_mgr, pbn);
 		ret = drm_dp_mst_allocate_vcpi(mst_mgr, mst_port, pbn, slots);
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 82add736e17d..3e7b7553cf4d 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3534,10 +3534,11 @@ EXPORT_SYMBOL(drm_dp_check_act_status);
  * drm_dp_calc_pbn_mode() - Calculate the PBN for a mode.
  * @clock: dot clock for the mode
  * @bpp: bpp for the mode.
+ * @dsc: DSC mode. If true, bpp has units of 1/16 of a bit per pixel
  *
  * This uses the formula in the spec to calculate the PBN value for a mode.
  */
-int drm_dp_calc_pbn_mode(int clock, int bpp)
+int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc)
 {
 	u64 kbps;
 	s64 peak_kbps;
@@ -3555,11 +3556,18 @@ int drm_dp_calc_pbn_mode(int clock, int bpp)
 	 * peak_kbps *= (1006/1000)
 	 * peak_kbps *= (64/54)
 	 * peak_kbps *= 8    convert to bytes
+	 *
+	 * If the bpp is in units of 1/16, further divide by 16. Put this
+	 * factor in the numerator rather than the denominator to avoid
+	 * integer overflow
 	 */
 
 	numerator = 64 * 1006;
 	denominator = 54 * 8 * 1000 * 1000;
 
+	if (dsc)
+		numerator /= 16;
+
 	kbps *= numerator;
 	peak_kbps = drm_fixp_from_fraction(kbps, denominator);
 
@@ -3570,19 +3578,19 @@ EXPORT_SYMBOL(drm_dp_calc_pbn_mode);
 static int test_calc_pbn_mode(void)
 {
 	int ret;
-	ret = drm_dp_calc_pbn_mode(154000, 30);
+	ret = drm_dp_calc_pbn_mode(154000, 30, false);
 	if (ret != 689) {
 		DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
 				154000, 30, 689, ret);
 		return -EINVAL;
 	}
-	ret = drm_dp_calc_pbn_mode(234000, 30);
+	ret = drm_dp_calc_pbn_mode(234000, 30, false);
 	if (ret != 1047) {
 		DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
 				234000, 30, 1047, ret);
 		return -EINVAL;
 	}
-	ret = drm_dp_calc_pbn_mode(297000, 24);
+	ret = drm_dp_calc_pbn_mode(297000, 24, false);
 	if (ret != 1063) {
 		DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
 				297000, 24, 1063, ret);
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 2c5ac3dd647f..4f17f61f4453 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -61,7 +61,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
 		crtc_state->pipe_bpp = bpp;
 
 		crtc_state->pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock,
-						       crtc_state->pipe_bpp);
+						       crtc_state->pipe_bpp, false);
 
 		slots = drm_dp_atomic_find_vcpi_slots(state, &intel_dp->mst_mgr,
 						      port, crtc_state->pbn);
diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 5c36c75232e6..c68783c1f3fa 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -782,7 +782,7 @@ nv50_msto_atomic_check(struct drm_encoder *encoder,
 			const int bpp = connector->display_info.bpc * 3;
 			const int clock = crtc_state->adjusted_mode.clock;
 
-			asyh->dp.pbn = drm_dp_calc_pbn_mode(clock, bpp);
+			asyh->dp.pbn = drm_dp_calc_pbn_mode(clock, bpp, false);
 		}
 
 		slots = drm_dp_atomic_find_vcpi_slots(state, &mstm->mgr,
diff --git a/drivers/gpu/drm/radeon/radeon_dp_mst.c b/drivers/gpu/drm/radeon/radeon_dp_mst.c
index 2994f07fbad9..c997f88218f2 100644
--- a/drivers/gpu/drm/radeon/radeon_dp_mst.c
+++ b/drivers/gpu/drm/radeon/radeon_dp_mst.c
@@ -514,7 +514,7 @@ static bool radeon_mst_mode_fixup(struct drm_encoder *encoder,
 
 	mst_enc = radeon_encoder->enc_priv;
 
-	mst_enc->pbn = drm_dp_calc_pbn_mode(adjusted_mode->clock, bpp);
+	mst_enc->pbn = drm_dp_calc_pbn_mode(adjusted_mode->clock, bpp, false);
 
 	mst_enc->primary->active_device = mst_enc->primary->devices & mst_enc->connector->devices;
 	DRM_DEBUG_KMS("setting active device to %08x from %08x %08x for encoder %d\n",
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 2ba6253ea6d3..9116b2c95239 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -610,8 +610,7 @@ bool drm_dp_mst_port_has_audio(struct drm_dp_mst_topology_mgr *mgr,
 struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port);
 
 
-int drm_dp_calc_pbn_mode(int clock, int bpp);
-
+int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc);
 
 bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 			      struct drm_dp_mst_port *port, int pbn, int slots);
-- 
2.17.1

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[PATCH v9 2/6] drm/dp_mst: Parse FEC capability on MST ports

[David Francis]

As of DP1.4, ENUM_PATH_RESOURCES returns a bit indicating
if FEC can be supported up to that point in the MST network.

The bit is the first byte of the ENUM_PATH_RESOURCES ack reply,
bottom-most bit (refer to section 2.11.9.4 of DP standard,
v1.4)

That value is needed for FEC and DSC support

Store it on drm_dp_mst_port

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 2 ++
 include/drm/drm_dp_mst_helper.h       | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 3e7b7553cf4d..9f3604355705 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -553,6 +553,7 @@ static bool drm_dp_sideband_parse_enum_path_resources_ack(struct drm_dp_sideband
 {
 	int idx = 1;
 	repmsg->u.path_resources.port_number = (raw->msg[idx] >> 4) & 0xf;
+	repmsg->u.path_resources.fec_capable = raw->msg[idx] & 0x1;
 	idx++;
 	if (idx > raw->curlen)
 		goto fail_len;
@@ -2183,6 +2184,7 @@ static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
 			DRM_DEBUG_KMS("enum path resources %d: %d %d\n", txmsg->reply.u.path_resources.port_number, txmsg->reply.u.path_resources.full_payload_bw_number,
 			       txmsg->reply.u.path_resources.avail_payload_bw_number);
 			port->available_pbn = txmsg->reply.u.path_resources.avail_payload_bw_number;
+			port->fec_capable = txmsg->reply.u.path_resources.fec_capable;
 		}
 	}
 
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 9116b2c95239..f113ae04fa88 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -108,6 +108,8 @@ struct drm_dp_mst_port {
 	 * audio-capable.
 	 */
 	bool has_audio;
+
+	bool fec_capable;
 };
 
 /**
@@ -312,6 +314,7 @@ struct drm_dp_port_number_req {
 
 struct drm_dp_enum_path_resources_ack_reply {
 	u8 port_number;
+	bool fec_capable;
 	u16 full_payload_bw_number;
 	u16 avail_payload_bw_number;
 };
-- 
2.17.1

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[PATCH v9 3/6] drm/dp_mst: Add MST support to DP DPCD R/W functions

[David Francis]

Instead of having drm_dp_dpcd_read/write and
drm_dp_mst_dpcd_read/write as entry points into the
aux code, have drm_dp_dpcd_read/write handle both.

This means that DRM drivers can make MST DPCD read/writes.

v2: Fix spacing
v3: Dump dpcd access on MST read/writes

Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
---
 drivers/gpu/drm/drm_dp_aux_dev.c | 12 ++----------
 drivers/gpu/drm/drm_dp_helper.c  | 30 ++++++++++++++++++++----------
 2 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_aux_dev.c b/drivers/gpu/drm/drm_dp_aux_dev.c
index 0cfb386754c3..418cad4f649a 100644
--- a/drivers/gpu/drm/drm_dp_aux_dev.c
+++ b/drivers/gpu/drm/drm_dp_aux_dev.c
@@ -163,11 +163,7 @@ static ssize_t auxdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 			break;
 		}
 
-		if (aux_dev->aux->is_remote)
-			res = drm_dp_mst_dpcd_read(aux_dev->aux, pos, buf,
-						   todo);
-		else
-			res = drm_dp_dpcd_read(aux_dev->aux, pos, buf, todo);
+		res = drm_dp_dpcd_read(aux_dev->aux, pos, buf, todo);
 
 		if (res <= 0)
 			break;
@@ -215,11 +211,7 @@ static ssize_t auxdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			break;
 		}
 
-		if (aux_dev->aux->is_remote)
-			res = drm_dp_mst_dpcd_write(aux_dev->aux, pos, buf,
-						    todo);
-		else
-			res = drm_dp_dpcd_write(aux_dev->aux, pos, buf, todo);
+		res = drm_dp_mst_dpcd_write(aux_dev->aux, pos, buf, todo);
 
 		if (res <= 0)
 			break;
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index ffc68d305afe..2cc21eff4cf3 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -30,6 +30,7 @@
 #include <linux/seq_file.h>
 
 #include <drm/drm_dp_helper.h>
+#include <drm/drm_dp_mst_helper.h>
 #include <drm/drm_print.h>
 #include <drm/drm_vblank.h>
 
@@ -251,7 +252,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 
 /**
  * drm_dp_dpcd_read() - read a series of bytes from the DPCD
- * @aux: DisplayPort AUX channel
+ * @aux: DisplayPort AUX channel (SST or MST)
  * @offset: address of the (first) register to read
  * @buffer: buffer to store the register values
  * @size: number of bytes in @buffer
@@ -280,13 +281,18 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
 	 * We just have to do it before any DPCD access and hope that the
 	 * monitor doesn't power down exactly after the throw away read.
 	 */
-	ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, DP_DPCD_REV, buffer,
-				 1);
-	if (ret != 1)
-		goto out;
+	if (!aux->is_remote) {
+		ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, DP_DPCD_REV,
+					 buffer, 1);
+		if (ret != 1)
+			goto out;
+	}
 
-	ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, buffer,
-				 size);
+	if (aux->is_remote)
+		ret = drm_dp_mst_dpcd_read(aux, offset, buffer, size);
+	else
+		ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset,
+					 buffer, size);
 
 out:
 	drm_dp_dump_access(aux, DP_AUX_NATIVE_READ, offset, buffer, ret);
@@ -296,7 +302,7 @@ EXPORT_SYMBOL(drm_dp_dpcd_read);
 
 /**
  * drm_dp_dpcd_write() - write a series of bytes to the DPCD
- * @aux: DisplayPort AUX channel
+ * @aux: DisplayPort AUX channel (SST or MST)
  * @offset: address of the (first) register to write
  * @buffer: buffer containing the values to write
  * @size: number of bytes in @buffer
@@ -313,8 +319,12 @@ ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
 {
 	int ret;
 
-	ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_WRITE, offset, buffer,
-				 size);
+	if (aux->is_remote)
+		ret = drm_dp_mst_dpcd_write(aux, offset, buffer, size);
+	else
+		ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_WRITE, offset,
+					 buffer, size);
+
 	drm_dp_dump_access(aux, DP_AUX_NATIVE_WRITE, offset, buffer, ret);
 	return ret;
 }
-- 
2.17.1

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[PATCH v9 4/6] drm/dp_mst: Fill branch->num_ports

[David Francis]

This field on drm_dp_mst_branch was never filled

It is initialized to zero when the port is kzallocced.
When a port is added to the list, increment num_ports,
and when a port is removed from the list, decrement num_ports.

v2: remember to decrement on port removal
v3: don't explicitly init to 0

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 9f3604355705..502923c24450 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1669,6 +1669,7 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 		mutex_lock(&mstb->mgr->lock);
 		drm_dp_mst_topology_get_port(port);
 		list_add(&port->next, &mstb->ports);
+		mstb->num_ports++;
 		mutex_unlock(&mstb->mgr->lock);
 	}
 
@@ -1703,6 +1704,7 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 			/* remove it from the port list */
 			mutex_lock(&mstb->mgr->lock);
 			list_del(&port->next);
+			mstb->num_ports--;
 			mutex_unlock(&mstb->mgr->lock);
 			/* drop port list reference */
 			drm_dp_mst_topology_put_port(port);
-- 
2.17.1

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[PATCH v9 5/6] drm/dp_mst: Add new quirk for Synaptics MST hubs

[David Francis]

Synaptics DP1.4 hubs (BRANCH_ID 0x90CC24) do not
support virtual DPCD registers, but do support DSC.
The DSC caps can be read from the physical aux,
like in SST DSC. These hubs have many different
DEVICE_IDs.  Add a new quirk to detect this case.

Cc: Lyude Paul <lyude@redhat.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 2 ++
 include/drm/drm_dp_helper.h     | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 2cc21eff4cf3..fc39323e7d52 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -1270,6 +1270,8 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
 	{ OUI(0x00, 0x10, 0xfa), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_NO_PSR) },
 	/* CH7511 seems to leave SINK_COUNT zeroed */
 	{ OUI(0x00, 0x00, 0x00), DEVICE_ID('C', 'H', '7', '5', '1', '1'), false, BIT(DP_DPCD_QUIRK_NO_SINK_COUNT) },
+	/* Synaptics DP1.4 MST hubs can support DSC without virtual DPCD */
+	{ OUI(0x90, 0xCC, 0x24), DEVICE_ID_ANY, true, BIT(DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) },
 };
 
 #undef OUI
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 8364502f92cf..a1331b08705f 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1434,6 +1434,13 @@ enum drm_dp_quirk {
 	 * The driver should ignore SINK_COUNT during detection.
 	 */
 	DP_DPCD_QUIRK_NO_SINK_COUNT,
+	/**
+	 * @DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD:
+	 *
+	 * The device supports MST DSC despite not supporting Virtual DPCD.
+	 * The DSC caps can be read from the physical aux instead.
+	 */
+	DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD,
 };
 
 /**
-- 
2.17.1

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[PATCH v9 6/6] drm/dp_mst: Add helpers for MST DSC and virtual DPCD aux

[David Francis]

Add drm_dp_mst_dsc_aux_for_port. To enable DSC, the DSC_ENABLED
register might have to be written on the leaf port's DPCD,
its parent's DPCD, or the MST manager's DPCD. This function
finds the correct aux for the job.

As part of this, add drm_dp_mst_is_virtual_dpcd. Virtual DPCD
is a DP feature new in DP v1.4, which exposes certain DPCD
registers on virtual ports.

v2: Remember to unlock mutex on all paths
v3: Refactor to match coding style and increase brevity

Cc: Lyude Paul <lyude@redhat.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 153 ++++++++++++++++++++++++++
 include/drm/drm_dp_mst_helper.h       |   2 +
 2 files changed, 155 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 502923c24450..e24dba276119 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -4150,3 +4150,156 @@ static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux)
 {
 	i2c_del_adapter(&aux->ddc);
 }
+
+/**
+ * drm_dp_mst_is_virtual_dpcd() - Is the given port a virtual DP Peer Device
+ * @port: The port to check
+ *
+ * A single physical MST hub object can be represented in the topology
+ * by multiple branches, with virtual ports between those branches.
+ *
+ * As of DP1.4, An MST hub with internal (virtual) ports must expose
+ * certain DPCD registers over those ports. See sections 2.6.1.1.1
+ * and 2.6.1.1.2 of Display Port specification v1.4 for details.
+ *
+ * May acquire mgr->lock
+ *
+ * Returns:
+ * true if the port is a virtual DP peer device, false otherwise
+ */
+static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
+{
+	struct drm_dp_mst_port *downstream_port;
+
+	if (!port || port->dpcd_rev < DP_DPCD_REV_14)
+		return false;
+
+	/* Virtual DP Sink (Internal Display Panel) */
+	if (port->port_num >= 8)
+		return true;
+
+	/* DP-to-HDMI Protocol Converter */
+	if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
+	    !port->mcs &&
+	    port->ldps)
+		return true;
+
+	/* DP-to-DP */
+	mutex_lock(&port->mgr->lock);
+	if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
+	    port->mstb &&
+	    port->mstb->num_ports == 2) {
+		list_for_each_entry(downstream_port, &port->mstb->ports, next) {
+			if (downstream_port->pdt == DP_PEER_DEVICE_SST_SINK &&
+			    !downstream_port->input) {
+				mutex_unlock(&port->mgr->lock);
+				return true;
+			}
+		}
+	}
+	mutex_unlock(&port->mgr->lock);
+
+	return false;
+}
+
+/**
+ * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
+ * @port: The port to check. A leaf of the MST tree with an attached display.
+ *
+ * Depending on the situation, DSC may be enabled via the endpoint aux,
+ * the immediately upstream aux, or the connector's physical aux.
+ *
+ * This is both the correct aux to read DSC_CAPABILITY and the
+ * correct aux to write DSC_ENABLED.
+ *
+ * This operation can be expensive (up to four aux reads), so
+ * the caller should cache the return.
+ *
+ * Returns:
+ * NULL if DSC cannot be enabled on this port, otherwise the aux device
+ */
+struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
+{
+	struct drm_dp_mst_port *immediate_upstream_port;
+	struct drm_dp_mst_port *fec_port;
+	struct drm_dp_desc *desc = NULL;
+
+	if (!port)
+		return NULL;
+
+	if (port->parent)
+		immediate_upstream_port = port->parent->port_parent;
+	else
+		immediate_upstream_port = NULL;
+
+	fec_port = immediate_upstream_port;
+	while (fec_port) {
+		/*
+		 * Each physical link (i.e. not a virtual port) between the
+		 * output and the primary device must support FEC
+		 */
+		if (!drm_dp_mst_is_virtual_dpcd(fec_port) &&
+				!fec_port->fec_capable)
+			return NULL;
+
+		fec_port = fec_port->parent->port_parent;
+	}
+
+	/* DP-to-DP peer device */
+	if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) {
+		u8 upstream_dsc;
+		u8 endpoint_dsc;
+		u8 endpoint_fec;
+
+		if (drm_dp_dpcd_read(&port->aux,
+				     DP_DSC_SUPPORT, &endpoint_dsc, 1) < 0)
+			return NULL;
+		if (drm_dp_dpcd_read(&port->aux,
+				     DP_FEC_CAPABILITY, &endpoint_fec, 1) < 0)
+			return NULL;
+		if (drm_dp_dpcd_read(&immediate_upstream_port->aux,
+				     DP_DSC_SUPPORT, &upstream_dsc, 1) < 0)
+			return NULL;
+
+		/* Enpoint decompression with DP-to-DP peer device */
+		if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
+		    (endpoint_fec & DP_FEC_CAPABLE) &&
+		    (upstream_dsc & 0x2) /* DSC passthrough */)
+			return &port->aux;
+
+		/* Virtual DPCD decompression with DP-to-DP peer device */
+		return &immediate_upstream_port->aux;
+	}
+
+	/* Virtual DPCD decompression with DP-to-HDMI or Virtual DP Sink */
+	if (drm_dp_mst_is_virtual_dpcd(port))
+		return &port->aux;
+
+	/*
+	 * Synaptics quirk
+	 * Applies to ports for which:
+	 * - Physical aux has Synaptics OUI
+	 * - DPv1.4 or higher
+	 * - Port is on primary branch device
+	 * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
+	 */
+	if (!drm_dp_read_desc(port->mgr->aux, desc, true))
+		return false;
+
+	if (drm_dp_has_quirk(desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD &&
+	    port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14) &&
+	    port->parent == port->mgr->mst_primary) {
+		u8 downstreamport;
+
+		drm_dp_dpcd_read(&port->aux, DP_DOWNSTREAMPORT_PRESENT,
+				 &downstreamport, 1);
+
+		if ((downstreamport & DP_DWN_STRM_PORT_PRESENT) &&
+		   ((downstreamport & DP_DWN_STRM_PORT_TYPE_MASK)
+		     != DP_DWN_STRM_PORT_TYPE_ANALOG))
+			return port->mgr->aux;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL(drm_dp_mst_dsc_aux_for_port);
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index f113ae04fa88..4cf738545dfb 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -673,6 +673,8 @@ int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
 void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
 void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
 
+struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port);
+
 extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
 
 /**
-- 
2.17.1

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Re: [PATCH v9 6/6] drm/dp_mst: Add helpers for MST DSC and virtual DPCD aux

[Jani Nikula]

On Tue, 27 Aug 2019, David Francis <David.Francis@amd.com> wrote:
> Add drm_dp_mst_dsc_aux_for_port. To enable DSC, the DSC_ENABLED
> register might have to be written on the leaf port's DPCD,
> its parent's DPCD, or the MST manager's DPCD. This function
> finds the correct aux for the job.
>
> As part of this, add drm_dp_mst_is_virtual_dpcd. Virtual DPCD
> is a DP feature new in DP v1.4, which exposes certain DPCD
> registers on virtual ports.
>
> v2: Remember to unlock mutex on all paths
> v3: Refactor to match coding style and increase brevity
>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
> Signed-off-by: David Francis <David.Francis@amd.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 153 ++++++++++++++++++++++++++
>  include/drm/drm_dp_mst_helper.h       |   2 +
>  2 files changed, 155 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 502923c24450..e24dba276119 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -4150,3 +4150,156 @@ static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux)
>  {
>  	i2c_del_adapter(&aux->ddc);
>  }
> +
> +/**
> + * drm_dp_mst_is_virtual_dpcd() - Is the given port a virtual DP Peer Device
> + * @port: The port to check
> + *
> + * A single physical MST hub object can be represented in the topology
> + * by multiple branches, with virtual ports between those branches.
> + *
> + * As of DP1.4, An MST hub with internal (virtual) ports must expose
> + * certain DPCD registers over those ports. See sections 2.6.1.1.1
> + * and 2.6.1.1.2 of Display Port specification v1.4 for details.
> + *
> + * May acquire mgr->lock
> + *
> + * Returns:
> + * true if the port is a virtual DP peer device, false otherwise
> + */
> +static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
> +{
> +	struct drm_dp_mst_port *downstream_port;
> +
> +	if (!port || port->dpcd_rev < DP_DPCD_REV_14)
> +		return false;
> +
> +	/* Virtual DP Sink (Internal Display Panel) */
> +	if (port->port_num >= 8)
> +		return true;
> +
> +	/* DP-to-HDMI Protocol Converter */
> +	if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
> +	    !port->mcs &&
> +	    port->ldps)
> +		return true;
> +
> +	/* DP-to-DP */
> +	mutex_lock(&port->mgr->lock);
> +	if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
> +	    port->mstb &&
> +	    port->mstb->num_ports == 2) {
> +		list_for_each_entry(downstream_port, &port->mstb->ports, next) {
> +			if (downstream_port->pdt == DP_PEER_DEVICE_SST_SINK &&
> +			    !downstream_port->input) {
> +				mutex_unlock(&port->mgr->lock);
> +				return true;
> +			}
> +		}
> +	}
> +	mutex_unlock(&port->mgr->lock);
> +
> +	return false;
> +}
> +
> +/**
> + * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
> + * @port: The port to check. A leaf of the MST tree with an attached display.
> + *
> + * Depending on the situation, DSC may be enabled via the endpoint aux,
> + * the immediately upstream aux, or the connector's physical aux.
> + *
> + * This is both the correct aux to read DSC_CAPABILITY and the
> + * correct aux to write DSC_ENABLED.
> + *
> + * This operation can be expensive (up to four aux reads), so
> + * the caller should cache the return.
> + *
> + * Returns:
> + * NULL if DSC cannot be enabled on this port, otherwise the aux device
> + */
> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
> +{
> +	struct drm_dp_mst_port *immediate_upstream_port;
> +	struct drm_dp_mst_port *fec_port;
> +	struct drm_dp_desc *desc = NULL;
> +
> +	if (!port)
> +		return NULL;
> +
> +	if (port->parent)
> +		immediate_upstream_port = port->parent->port_parent;
> +	else
> +		immediate_upstream_port = NULL;
> +
> +	fec_port = immediate_upstream_port;
> +	while (fec_port) {
> +		/*
> +		 * Each physical link (i.e. not a virtual port) between the
> +		 * output and the primary device must support FEC
> +		 */
> +		if (!drm_dp_mst_is_virtual_dpcd(fec_port) &&
> +				!fec_port->fec_capable)
> +			return NULL;
> +
> +		fec_port = fec_port->parent->port_parent;
> +	}
> +
> +	/* DP-to-DP peer device */
> +	if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) {
> +		u8 upstream_dsc;
> +		u8 endpoint_dsc;
> +		u8 endpoint_fec;
> +
> +		if (drm_dp_dpcd_read(&port->aux,
> +				     DP_DSC_SUPPORT, &endpoint_dsc, 1) < 0)
> +			return NULL;
> +		if (drm_dp_dpcd_read(&port->aux,
> +				     DP_FEC_CAPABILITY, &endpoint_fec, 1) < 0)
> +			return NULL;
> +		if (drm_dp_dpcd_read(&immediate_upstream_port->aux,
> +				     DP_DSC_SUPPORT, &upstream_dsc, 1) < 0)
> +			return NULL;
> +
> +		/* Enpoint decompression with DP-to-DP peer device */
> +		if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
> +		    (endpoint_fec & DP_FEC_CAPABLE) &&
> +		    (upstream_dsc & 0x2) /* DSC passthrough */)
> +			return &port->aux;
> +
> +		/* Virtual DPCD decompression with DP-to-DP peer device */
> +		return &immediate_upstream_port->aux;
> +	}
> +
> +	/* Virtual DPCD decompression with DP-to-HDMI or Virtual DP Sink */
> +	if (drm_dp_mst_is_virtual_dpcd(port))
> +		return &port->aux;
> +
> +	/*
> +	 * Synaptics quirk
> +	 * Applies to ports for which:
> +	 * - Physical aux has Synaptics OUI
> +	 * - DPv1.4 or higher
> +	 * - Port is on primary branch device
> +	 * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
> +	 */
> +	if (!drm_dp_read_desc(port->mgr->aux, desc, true))
> +		return false;
> +
> +	if (drm_dp_has_quirk(desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD &&
> +	    port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14) &&
> +	    port->parent == port->mgr->mst_primary) {
> +		u8 downstreamport;
> +
> +		drm_dp_dpcd_read(&port->aux, DP_DOWNSTREAMPORT_PRESENT,
> +				 &downstreamport, 1);
> +
> +		if ((downstreamport & DP_DWN_STRM_PORT_PRESENT) &&
> +		   ((downstreamport & DP_DWN_STRM_PORT_TYPE_MASK)
> +		     != DP_DWN_STRM_PORT_TYPE_ANALOG))
> +			return port->mgr->aux;
> +	}

I would've put the quirk definition from patch 5 and the quirk handling
above together into a separate patch. The current patch would be about
how things should work in theory, and another patch on top would be
about how reality interferes with theory, and you have to quirk stuff to
make it actually work.

The whole point about splitting the quirk off was that it's a separate
functional change. What if the quirk turns out to be a mistake?  Just
revert the whole thing. That would be impossible with this split.

I don't know if I care enough to insist. *shrug*


BR,
Jani.



> +
> +	return NULL;
> +}
> +EXPORT_SYMBOL(drm_dp_mst_dsc_aux_for_port);
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index f113ae04fa88..4cf738545dfb 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -673,6 +673,8 @@ int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
>  void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
>  void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
>  
> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port);
> +
>  extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
>  
>  /**

-- 
Jani Nikula, Intel Open Source Graphics Center
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Re: [PATCH v9 6/6] drm/dp_mst: Add helpers for MST DSC and virtual DPCD aux

[Francis, David]

>> Add drm_dp_mst_dsc_aux_for_port. To enable DSC, the DSC_ENABLED
>> register might have to be written on the leaf port's DPCD,
>> its parent's DPCD, or the MST manager's DPCD. This function
>> finds the correct aux for the job.
>>
>> As part of this, add drm_dp_mst_is_virtual_dpcd. Virtual DPCD
>> is a DP feature new in DP v1.4, which exposes certain DPCD
>> registers on virtual ports.
>>
>> v2: Remember to unlock mutex on all paths
>> v3: Refactor to match coding style and increase brevity
>>
>> Cc: Lyude Paul <lyude@redhat.com>
>> Cc: Jani Nikula <jani.nikula@linux.intel.com>
>> Cc: Harry Wentland <harry.wentland@amd.com>
>> Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
>> Signed-off-by: David Francis <David.Francis@amd.com>
>> ---
>>  drivers/gpu/drm/drm_dp_mst_topology.c | 153 ++++++++++++++++++++++++++
>>  include/drm/drm_dp_mst_helper.h       |   2 +
>>  2 files changed, 155 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
>> index 502923c24450..e24dba276119 100644
>> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
>> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
>> @@ -4150,3 +4150,156 @@ static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux)
>>  {
>>        i2c_del_adapter(&aux->ddc);
>>  }
>> +
>> +/**
>> + * drm_dp_mst_is_virtual_dpcd() - Is the given port a virtual DP Peer Device
>> + * @port: The port to check
>> + *
>> + * A single physical MST hub object can be represented in the topology
>> + * by multiple branches, with virtual ports between those branches.
>> + *
>> + * As of DP1.4, An MST hub with internal (virtual) ports must expose
>> + * certain DPCD registers over those ports. See sections 2.6.1.1.1
>> + * and 2.6.1.1.2 of Display Port specification v1.4 for details.
>> + *
>> + * May acquire mgr->lock
>> + *
>> + * Returns:
>> + * true if the port is a virtual DP peer device, false otherwise
>> + */
>> +static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
>> +{
>> +     struct drm_dp_mst_port *downstream_port;
>> +
>> +     if (!port || port->dpcd_rev < DP_DPCD_REV_14)
>> +             return false;
>> +
>> +     /* Virtual DP Sink (Internal Display Panel) */
>> +     if (port->port_num >= 8)
>> +             return true;
>> +
>> +     /* DP-to-HDMI Protocol Converter */
>> +     if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
>> +         !port->mcs &&
>> +         port->ldps)
>> +             return true;
>> +
>> +     /* DP-to-DP */
>> +     mutex_lock(&port->mgr->lock);
>> +     if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
>> +         port->mstb &&
>> +         port->mstb->num_ports == 2) {
>> +             list_for_each_entry(downstream_port, &port->mstb->ports, next) {
>> +                     if (downstream_port->pdt == DP_PEER_DEVICE_SST_SINK &&
>> +                         !downstream_port->input) {
>> +                             mutex_unlock(&port->mgr->lock);
>> +                             return true;
>> +                     }
>> +             }
>> +     }
>> +     mutex_unlock(&port->mgr->lock);
>> +
>> +     return false;
>> +}
>> +
>> +/**
>> + * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
>> + * @port: The port to check. A leaf of the MST tree with an attached display.
>> + *
>> + * Depending on the situation, DSC may be enabled via the endpoint aux,
>> + * the immediately upstream aux, or the connector's physical aux.
>> + *
>> + * This is both the correct aux to read DSC_CAPABILITY and the
>> + * correct aux to write DSC_ENABLED.
>> + *
>> + * This operation can be expensive (up to four aux reads), so
>> + * the caller should cache the return.
>> + *
>> + * Returns:
>> + * NULL if DSC cannot be enabled on this port, otherwise the aux device
>> + */
>> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
>> +{
>> +     struct drm_dp_mst_port *immediate_upstream_port;
>> +     struct drm_dp_mst_port *fec_port;
>> +     struct drm_dp_desc *desc = NULL;
>> +
>> +     if (!port)
>> +             return NULL;
>> +
>> +     if (port->parent)
>> +             immediate_upstream_port = port->parent->port_parent;
>> +     else
>> +             immediate_upstream_port = NULL;
>> +
>> +     fec_port = immediate_upstream_port;
>> +     while (fec_port) {
>> +             /*
>> +              * Each physical link (i.e. not a virtual port) between the
>> +              * output and the primary device must support FEC
>> +              */
>> +             if (!drm_dp_mst_is_virtual_dpcd(fec_port) &&
>> +                             !fec_port->fec_capable)
>> +                     return NULL;
>> +
>> +             fec_port = fec_port->parent->port_parent;
>> +     }
>> +
>> +     /* DP-to-DP peer device */
>> +     if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) {
>> +             u8 upstream_dsc;
>> +             u8 endpoint_dsc;
>> +             u8 endpoint_fec;
>> +
>> +             if (drm_dp_dpcd_read(&port->aux,
>> +                                  DP_DSC_SUPPORT, &endpoint_dsc, 1) < 0)
>> +                     return NULL;
>> +             if (drm_dp_dpcd_read(&port->aux,
>> +                                  DP_FEC_CAPABILITY, &endpoint_fec, 1) < 0)
>> +                     return NULL;
>> +             if (drm_dp_dpcd_read(&immediate_upstream_port->aux,
>> +                                  DP_DSC_SUPPORT, &upstream_dsc, 1) < 0)
>> +                     return NULL;
>> +
>> +             /* Enpoint decompression with DP-to-DP peer device */
>> +             if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
>> +                 (endpoint_fec & DP_FEC_CAPABLE) &&
>> +                 (upstream_dsc & 0x2) /* DSC passthrough */)
>> +                     return &port->aux;
>> +
>> +             /* Virtual DPCD decompression with DP-to-DP peer device */
>> +             return &immediate_upstream_port->aux;
>> +     }
>> +
>> +     /* Virtual DPCD decompression with DP-to-HDMI or Virtual DP Sink */
>> +     if (drm_dp_mst_is_virtual_dpcd(port))
>> +             return &port->aux;
>> +
>> +     /*
>> +      * Synaptics quirk
>> +      * Applies to ports for which:
>> +      * - Physical aux has Synaptics OUI
>> +      * - DPv1.4 or higher
>> +      * - Port is on primary branch device
>> +      * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
>> +      */
>> +     if (!drm_dp_read_desc(port->mgr->aux, desc, true))
>> +             return false;
>> +
>> +     if (drm_dp_has_quirk(desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD &&
>> +         port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14) &&
>> +         port->parent == port->mgr->mst_primary) {
>> +             u8 downstreamport;
>> +
>> +             drm_dp_dpcd_read(&port->aux, DP_DOWNSTREAMPORT_PRESENT,
>> +                              &downstreamport, 1);
>> +
>> +             if ((downstreamport & DP_DWN_STRM_PORT_PRESENT) &&
>> +                ((downstreamport & DP_DWN_STRM_PORT_TYPE_MASK)
>> +                  != DP_DWN_STRM_PORT_TYPE_ANALOG))
>> +                     return port->mgr->aux;
>> +     }
>
>I would've put the quirk definition from patch 5 and the quirk handling
>above together into a separate patch. The current patch would be about
>how things should work in theory, and another patch on top would be
>about how reality interferes with theory, and you have to quirk stuff to
>make it actually work.
>
>The whole point about splitting the quirk off was that it's a separate
>functional change. What if the quirk turns out to be a mistake?  Just
>revert the whole thing. That would be impossible with this split.
>
>I don't know if I care enough to insist. *shrug*
>

No, that's a good point.  Fixing this for v10

>
>BR,
>Jani.
>
>
>
>> +
>> +     return NULL;
>> +}
>> +EXPORT_SYMBOL(drm_dp_mst_dsc_aux_for_port);
>> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
>> index f113ae04fa88..4cf738545dfb 100644
>> --- a/include/drm/drm_dp_mst_helper.h
>> +++ b/include/drm/drm_dp_mst_helper.h
>> @@ -673,6 +673,8 @@ int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
>>  void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
>>  void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
>>
>> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port);
>> +
>>  extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
>>
>>  /**
>
>--
>Jani Nikula, Intel Open Source Graphics Center

________________________________________
From: Jani Nikula <jani.nikula@linux.intel.com>
Sent: August 27, 2019 10:52 AM
To: Francis, David; dri-devel@lists.freedesktop.org
Cc: Francis, David; Lyude Paul; Wentland, Harry
Subject: Re: [PATCH v9 6/6] drm/dp_mst: Add helpers for MST DSC and virtual DPCD aux

On Tue, 27 Aug 2019, David Francis <David.Francis@amd.com> wrote:
> Add drm_dp_mst_dsc_aux_for_port. To enable DSC, the DSC_ENABLED
> register might have to be written on the leaf port's DPCD,
> its parent's DPCD, or the MST manager's DPCD. This function
> finds the correct aux for the job.
>
> As part of this, add drm_dp_mst_is_virtual_dpcd. Virtual DPCD
> is a DP feature new in DP v1.4, which exposes certain DPCD
> registers on virtual ports.
>
> v2: Remember to unlock mutex on all paths
> v3: Refactor to match coding style and increase brevity
>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
> Signed-off-by: David Francis <David.Francis@amd.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 153 ++++++++++++++++++++++++++
>  include/drm/drm_dp_mst_helper.h       |   2 +
>  2 files changed, 155 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 502923c24450..e24dba276119 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -4150,3 +4150,156 @@ static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux)
>  {
>       i2c_del_adapter(&aux->ddc);
>  }
> +
> +/**
> + * drm_dp_mst_is_virtual_dpcd() - Is the given port a virtual DP Peer Device
> + * @port: The port to check
> + *
> + * A single physical MST hub object can be represented in the topology
> + * by multiple branches, with virtual ports between those branches.
> + *
> + * As of DP1.4, An MST hub with internal (virtual) ports must expose
> + * certain DPCD registers over those ports. See sections 2.6.1.1.1
> + * and 2.6.1.1.2 of Display Port specification v1.4 for details.
> + *
> + * May acquire mgr->lock
> + *
> + * Returns:
> + * true if the port is a virtual DP peer device, false otherwise
> + */
> +static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
> +{
> +     struct drm_dp_mst_port *downstream_port;
> +
> +     if (!port || port->dpcd_rev < DP_DPCD_REV_14)
> +             return false;
> +
> +     /* Virtual DP Sink (Internal Display Panel) */
> +     if (port->port_num >= 8)
> +             return true;
> +
> +     /* DP-to-HDMI Protocol Converter */
> +     if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
> +         !port->mcs &&
> +         port->ldps)
> +             return true;
> +
> +     /* DP-to-DP */
> +     mutex_lock(&port->mgr->lock);
> +     if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
> +         port->mstb &&
> +         port->mstb->num_ports == 2) {
> +             list_for_each_entry(downstream_port, &port->mstb->ports, next) {
> +                     if (downstream_port->pdt == DP_PEER_DEVICE_SST_SINK &&
> +                         !downstream_port->input) {
> +                             mutex_unlock(&port->mgr->lock);
> +                             return true;
> +                     }
> +             }
> +     }
> +     mutex_unlock(&port->mgr->lock);
> +
> +     return false;
> +}
> +
> +/**
> + * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
> + * @port: The port to check. A leaf of the MST tree with an attached display.
> + *
> + * Depending on the situation, DSC may be enabled via the endpoint aux,
> + * the immediately upstream aux, or the connector's physical aux.
> + *
> + * This is both the correct aux to read DSC_CAPABILITY and the
> + * correct aux to write DSC_ENABLED.
> + *
> + * This operation can be expensive (up to four aux reads), so
> + * the caller should cache the return.
> + *
> + * Returns:
> + * NULL if DSC cannot be enabled on this port, otherwise the aux device
> + */
> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
> +{
> +     struct drm_dp_mst_port *immediate_upstream_port;
> +     struct drm_dp_mst_port *fec_port;
> +     struct drm_dp_desc *desc = NULL;
> +
> +     if (!port)
> +             return NULL;
> +
> +     if (port->parent)
> +             immediate_upstream_port = port->parent->port_parent;
> +     else
> +             immediate_upstream_port = NULL;
> +
> +     fec_port = immediate_upstream_port;
> +     while (fec_port) {
> +             /*
> +              * Each physical link (i.e. not a virtual port) between the
> +              * output and the primary device must support FEC
> +              */
> +             if (!drm_dp_mst_is_virtual_dpcd(fec_port) &&
> +                             !fec_port->fec_capable)
> +                     return NULL;
> +
> +             fec_port = fec_port->parent->port_parent;
> +     }
> +
> +     /* DP-to-DP peer device */
> +     if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) {
> +             u8 upstream_dsc;
> +             u8 endpoint_dsc;
> +             u8 endpoint_fec;
> +
> +             if (drm_dp_dpcd_read(&port->aux,
> +                                  DP_DSC_SUPPORT, &endpoint_dsc, 1) < 0)
> +                     return NULL;
> +             if (drm_dp_dpcd_read(&port->aux,
> +                                  DP_FEC_CAPABILITY, &endpoint_fec, 1) < 0)
> +                     return NULL;
> +             if (drm_dp_dpcd_read(&immediate_upstream_port->aux,
> +                                  DP_DSC_SUPPORT, &upstream_dsc, 1) < 0)
> +                     return NULL;
> +
> +             /* Enpoint decompression with DP-to-DP peer device */
> +             if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
> +                 (endpoint_fec & DP_FEC_CAPABLE) &&
> +                 (upstream_dsc & 0x2) /* DSC passthrough */)
> +                     return &port->aux;
> +
> +             /* Virtual DPCD decompression with DP-to-DP peer device */
> +             return &immediate_upstream_port->aux;
> +     }
> +
> +     /* Virtual DPCD decompression with DP-to-HDMI or Virtual DP Sink */
> +     if (drm_dp_mst_is_virtual_dpcd(port))
> +             return &port->aux;
> +
> +     /*
> +      * Synaptics quirk
> +      * Applies to ports for which:
> +      * - Physical aux has Synaptics OUI
> +      * - DPv1.4 or higher
> +      * - Port is on primary branch device
> +      * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
> +      */
> +     if (!drm_dp_read_desc(port->mgr->aux, desc, true))
> +             return false;
> +
> +     if (drm_dp_has_quirk(desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD &&
> +         port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14) &&
> +         port->parent == port->mgr->mst_primary) {
> +             u8 downstreamport;
> +
> +             drm_dp_dpcd_read(&port->aux, DP_DOWNSTREAMPORT_PRESENT,
> +                              &downstreamport, 1);
> +
> +             if ((downstreamport & DP_DWN_STRM_PORT_PRESENT) &&
> +                ((downstreamport & DP_DWN_STRM_PORT_TYPE_MASK)
> +                  != DP_DWN_STRM_PORT_TYPE_ANALOG))
> +                     return port->mgr->aux;
> +     }

I would've put the quirk definition from patch 5 and the quirk handling
above together into a separate patch. The current patch would be about
how things should work in theory, and another patch on top would be
about how reality interferes with theory, and you have to quirk stuff to
make it actually work.

The whole point about splitting the quirk off was that it's a separate
functional change. What if the quirk turns out to be a mistake?  Just
revert the whole thing. That would be impossible with this split.

I don't know if I care enough to insist. *shrug*


BR,
Jani.



> +
> +     return NULL;
> +}
> +EXPORT_SYMBOL(drm_dp_mst_dsc_aux_for_port);
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index f113ae04fa88..4cf738545dfb 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -673,6 +673,8 @@ int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
>  void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
>  void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
>
> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port);
> +
>  extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
>
>  /**

--
Jani Nikula, Intel Open Source Graphics Center
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