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 right-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 capabilities 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@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220322143844.42616-1-imre.deak@intel.com
}
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.
* 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
*
* 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);
}
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;
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);
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;
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,
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);
}
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;
}
*/
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;
+
+ if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
+ return -EIO;
- /* The DPTX shall read the DPRX caps after LTTPR detection. */
+ 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;
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]);
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