[Intel-gfx] [PATCH v2] drm/i915: Add a DP1.2 compatible way to read LTTPR capabilities
Imre Deak
imre.deak at intel.com
Tue Mar 22 14:38:44 UTC 2022
At least some DELL monitors (P2715Q) with DPCD_REV 1.2 return corrupted
DPCD register values when reading from the 0xF0000- LTTPR range with an
AUX transaction block size bigger than 1. The DP standard requires 0 to
be returned - as for any other reserved/invalid addresses - but these
monitors return the DPCD_REV register value repeated in each byte of the
read buffer. This will in turn corrupt the values returned by the LTTPRs
between the source and the monitor: LTTPRs must adjust the values they
read from the downstream DPRX, for instance left-shift/init the
downstream DP_PHY_REPEATER_CNT value. Since the value returned by the
monitor's DPRX is non-zero the adjusted values will be corrupt.
Reading the LTTPR registers one-by-one instead of reading all of them
with a single AUX transfer works around the issue.
According to the DP standard's 0xF0000 register description:
"LTTPR-related registers at DPCD Addresses F0000h through F02FFh are
valid only for DPCD r1.4 (or higher)." While it's unclear if DPCD r1.4
refers to the DPCD_REV or to the
LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV register (tickets filed
at the VESA site to clarify this haven't been addressed), one
possibility is that it's a restriction due to non-compliant monitors
described above. Disabling the non-transparent LTTPR mode for all such
monitors is not a viable solution: the transparent LTTPR mode has its
own issue causing link training failures and this would affect a lot of
monitors in use with DPCD_REV < 1.4. Instead this patch works around
the problem by reading the LTTPR common and PHY cap registers one-by-one
for any monitor with a DPCD_REV < 1.4.
The standard requires the DPCD capabilites to be read after the LTTPR
common capabilities are read, so re-read the DPCD capabilities after
the LTTPR common and PHY caps were read out.
v2:
- Use for instead of a while loop. (Ville)
- Add to code comment the monitor model with the problem.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4531
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
drivers/gpu/drm/dp/drm_dp.c | 57 ++++++++++++-------
.../drm/i915/display/intel_dp_link_training.c | 30 +++++++---
include/drm/dp/drm_dp_helper.h | 2 +
3 files changed, 58 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c
index 703972ae14c64..58744f83931af 100644
--- a/drivers/gpu/drm/dp/drm_dp.c
+++ b/drivers/gpu/drm/dp/drm_dp.c
@@ -2390,9 +2390,35 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S
}
EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
+static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address,
+ u8 *buf, int buf_size)
+{
+ /*
+ * At least the DELL P2715Q monitor with a DPCD_REV < 0x14 returns
+ * corrupted values when reading from the 0xF0000- range with a block
+ * size bigger than 1.
+ */
+ int block_size = dpcd[DP_DPCD_REV] < 0x14 ? 1 : buf_size;
+ int offset;
+ int ret;
+
+ for (offset = 0; offset < buf_size; offset += block_size) {
+ ret = drm_dp_dpcd_read(aux,
+ address + offset,
+ &buf[offset], block_size);
+ if (ret < 0)
+ return ret;
+
+ WARN_ON(ret != block_size);
+ }
+
+ return 0;
+}
+
/**
* drm_dp_read_lttpr_common_caps - read the LTTPR common capabilities
* @aux: DisplayPort AUX channel
+ * @dpcd: DisplayPort configuration data
* @caps: buffer to return the capability info in
*
* Read capabilities common to all LTTPRs.
@@ -2400,25 +2426,19 @@ EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
* Returns 0 on success or a negative error code on failure.
*/
int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux,
+ const u8 dpcd[DP_RECEIVER_CAP_SIZE],
u8 caps[DP_LTTPR_COMMON_CAP_SIZE])
{
- int ret;
-
- ret = drm_dp_dpcd_read(aux,
- DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV,
- caps, DP_LTTPR_COMMON_CAP_SIZE);
- if (ret < 0)
- return ret;
-
- WARN_ON(ret != DP_LTTPR_COMMON_CAP_SIZE);
-
- return 0;
+ return drm_dp_read_lttpr_regs(aux, dpcd,
+ DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV,
+ caps, DP_LTTPR_COMMON_CAP_SIZE);
}
EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps);
/**
* drm_dp_read_lttpr_phy_caps - read the capabilities for a given LTTPR PHY
* @aux: DisplayPort AUX channel
+ * @dpcd: DisplayPort configuration data
* @dp_phy: LTTPR PHY to read the capabilities for
* @caps: buffer to return the capability info in
*
@@ -2427,20 +2447,13 @@ EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps);
* Returns 0 on success or a negative error code on failure.
*/
int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux,
+ const u8 dpcd[DP_RECEIVER_CAP_SIZE],
enum drm_dp_phy dp_phy,
u8 caps[DP_LTTPR_PHY_CAP_SIZE])
{
- int ret;
-
- ret = drm_dp_dpcd_read(aux,
- DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy),
- caps, DP_LTTPR_PHY_CAP_SIZE);
- if (ret < 0)
- return ret;
-
- WARN_ON(ret != DP_LTTPR_PHY_CAP_SIZE);
-
- return 0;
+ return drm_dp_read_lttpr_regs(aux, dpcd,
+ DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy),
+ caps, DP_LTTPR_PHY_CAP_SIZE);
}
EXPORT_SYMBOL(drm_dp_read_lttpr_phy_caps);
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
index 5d98773efd1b3..fbee20a76cf44 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -55,6 +55,7 @@ static u8 *intel_dp_lttpr_phy_caps(struct intel_dp *intel_dp,
}
static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
+ const u8 dpcd[DP_RECEIVER_CAP_SIZE],
enum drm_dp_phy dp_phy)
{
struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
@@ -63,7 +64,7 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name));
- if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dp_phy, phy_caps) < 0) {
+ if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dpcd, dp_phy, phy_caps) < 0) {
drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
"[ENCODER:%d:%s][%s] failed to read the PHY caps\n",
encoder->base.base.id, encoder->base.name, phy_name);
@@ -77,10 +78,11 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
phy_caps);
}
-static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp)
+static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
{
struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
struct drm_i915_private *i915 = to_i915(encoder->base.dev);
+ int ret;
if (intel_dp_is_edp(intel_dp))
return false;
@@ -92,8 +94,9 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp)
if (DISPLAY_VER(i915) < 10 || IS_GEMINILAKE(i915))
return false;
- if (drm_dp_read_lttpr_common_caps(&intel_dp->aux,
- intel_dp->lttpr_common_caps) < 0)
+ ret = drm_dp_read_lttpr_common_caps(&intel_dp->aux, dpcd,
+ intel_dp->lttpr_common_caps);
+ if (ret < 0)
goto reset_caps;
drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
@@ -122,14 +125,14 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable)
return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1;
}
-static int intel_dp_init_lttpr(struct intel_dp *intel_dp)
+static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
{
struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
struct drm_i915_private *i915 = to_i915(encoder->base.dev);
int lttpr_count;
int i;
- if (!intel_dp_read_lttpr_common_caps(intel_dp))
+ if (!intel_dp_read_lttpr_common_caps(intel_dp, dpcd))
return 0;
lttpr_count = drm_dp_lttpr_count(intel_dp->lttpr_common_caps);
@@ -168,7 +171,7 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp)
}
for (i = 0; i < lttpr_count; i++)
- intel_dp_read_lttpr_phy_caps(intel_dp, DP_PHY_LTTPR(i));
+ intel_dp_read_lttpr_phy_caps(intel_dp, dpcd, DP_PHY_LTTPR(i));
return lttpr_count;
}
@@ -193,9 +196,18 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp)
*/
int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp)
{
- int lttpr_count = intel_dp_init_lttpr(intel_dp);
+ u8 dpcd[DP_RECEIVER_CAP_SIZE];
+ int lttpr_count;
- /* The DPTX shall read the DPRX caps after LTTPR detection. */
+ if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
+ return -EIO;
+
+ lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd);
+
+ /*
+ * The DPTX shall read the DPRX caps after LTTPR detection, so re-read
+ * it here.
+ */
if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd)) {
intel_dp_reset_lttpr_common_caps(intel_dp);
return -EIO;
diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h
index 51e02cf75277e..1eccd97419436 100644
--- a/include/drm/dp/drm_dp_helper.h
+++ b/include/drm/dp/drm_dp_helper.h
@@ -2148,8 +2148,10 @@ bool drm_dp_read_sink_count_cap(struct drm_connector *connector,
int drm_dp_read_sink_count(struct drm_dp_aux *aux);
int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux,
+ const u8 dpcd[DP_RECEIVER_CAP_SIZE],
u8 caps[DP_LTTPR_COMMON_CAP_SIZE]);
int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux,
+ const u8 dpcd[DP_RECEIVER_CAP_SIZE],
enum drm_dp_phy dp_phy,
u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
int drm_dp_lttpr_count(const u8 cap[DP_LTTPR_COMMON_CAP_SIZE]);
--
2.30.2
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