[PATCH 05/10] drm: Add supporting structure for Displayport Link CTS test 4.2.2.6

Todd Previte
2015-04-15T15:38:42Z

Displayport compliance test 4.2.2.6 requires that a source device be capable of
detecting a corrupt EDID. The test specification states that the sink device
sets up the EDID with an invalid checksum. To do this, the sink sets up an
invalid EDID header, expecting the source device to generate the checksum and
compare it to the value stored in the last byte of the block data.

Unfortunately, the DRM EDID reading and parsing functions are actually too good
in this case; the header is fixed before the checksum is computed and thus the
code never sees the invalid checksum. This results in a failure to pass the
compliance test.

To correct this issue, a checksum is generated when the EDID header is detected
as corrupted. If the checksum is invalid, it sets the header_corrupt flag and
logs the errors. In the case of a more seriously damaged header (fixup score
less than the threshold) the code does not generate the checksum but does set
the header_corrupt flag.

V2:
- Removed the static bool global
- Added a bool to the drm_connector struct to reaplce the static one for
holding the status of raw edid header corruption detection
- Modified the function signature of the is_valid function to take an
additional parameter to store the corruption detected value
- Fixed the other callers of the above is_valid function
V3:
- Updated the commit message to be more clear about what and why this
patch does what it does.
- Added comment in code to clarify the operations there
- Removed compliance variable and check_link_status update; those
have been moved to a later patch
- Removed variable assignment from the bottom of the test handler
V4:
- Removed i915 tag from subject line as the patch is not i915-specific
V5:
- Moved code causing a compilation error to this patch where the variable
is actually declared
- Maintained blank lines / spacing so as to not contaminate the patch
V6:
- Removed extra debug messages
- Added documentation to for the added parameter on drm_edid_block_valid
- Fixed more whitespace issues in check_link_status
- Added a clear of the header_corrupt flag to the end of the test handler
in intel_dp.c
- Changed the usage of the new function prototype in several places to use
NULL where it is not needed by compliance testing

Signed-off-by: Todd Previte <tprevite@gmail.com>
Cc: dri-devel@lists.freedesktop.org
---
drivers/gpu/drm/drm_edid.c | 30 ++++++++++++++++++++++++++----
drivers/gpu/drm/drm_edid_load.c | 7 +++++--
drivers/gpu/drm/i915/intel_dp.c | 6 +++++-
include/drm/drm_crtc.h | 8 +++++++-
4 files changed, 43 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 53bc7a6..1ed18f5 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1041,13 +1041,15 @@ static bool drm_edid_is_zero(const u8 *in_edid, int length)
* @raw_edid: pointer to raw EDID block
* @block: type of block to validate (0 for base, extension otherwise)
* @print_bad_edid: if true, dump bad EDID blocks to the console
+ * @header_corrupt: if true, the header or checksum is invalid
*
* Validate a base or extension EDID block and optionally dump bad blocks to
* the console.
*
* Return: True if the block is valid, false otherwise.
*/
-bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid)
+bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid,
+ bool *header_corrupt)
{
u8 csum;
struct edid *edid = (struct edid *)raw_edid;
@@ -1062,9 +1064,25 @@ bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid)
int score = drm_edid_header_is_valid(raw_edid);
if (score == 8) ;
else if (score >= edid_fixup) {
+ /* Displayport Link CTS Core 1.2 rev1.1 test 4.2.2.6
+ * In order to properly generate the invalid checksum
+ * required for this test, it must be generated using
+ * the raw EDID data. Otherwise, the fix-up code here
+ * will correct the problem, the checksum is correct
+ * and the test fails
+ */
+ csum = drm_edid_block_checksum(raw_edid);
+ if (csum) {
+ if (header_corrupt)
+ *header_corrupt = 1;
+ }
DRM_DEBUG("Fixing EDID header, your hardware may be failing\n");
memcpy(raw_edid, edid_header, sizeof(edid_header));
} else {
+ if (header_corrupt) {
+ DRM_DEBUG_DRIVER("Invalid EDID header\n");
+ *header_corrupt = 1;
+ }
goto bad;
}
}
@@ -1129,7 +1147,7 @@ bool drm_edid_is_valid(struct edid *edid)
return false;

for (i = 0; i <= edid->extensions; i++)
- if (!drm_edid_block_valid(raw + i * EDID_LENGTH, i, true))
+ if (!drm_edid_block_valid(raw + i * EDID_LENGTH, i, true, NULL))
return false;

return true;
@@ -1232,7 +1250,8 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
for (i = 0; i < 4; i++) {
if (get_edid_block(data, block, 0, EDID_LENGTH))
goto out;
- if (drm_edid_block_valid(block, 0, print_bad_edid))
+ if (drm_edid_block_valid(block, 0, print_bad_edid,
+ &connector->edid_header_corrupt))
break;
if (i == 0 && drm_edid_is_zero(block, EDID_LENGTH)) {
connector->null_edid_counter++;
@@ -1257,7 +1276,10 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
block + (valid_extensions + 1) * EDID_LENGTH,
j, EDID_LENGTH))
goto out;
- if (drm_edid_block_valid(block + (valid_extensions + 1) * EDID_LENGTH, j, print_bad_edid)) {
+ if (drm_edid_block_valid(block + (valid_extensions + 1)
+ * EDID_LENGTH, j,
+ print_bad_edid,
+ NULL)) {
valid_extensions++;
break;
}
diff --git a/drivers/gpu/drm/drm_edid_load.c b/drivers/gpu/drm/drm_edid_load.c
index 4c0aa97..48b48e8 100644
--- a/drivers/gpu/drm/drm_edid_load.c
+++ b/drivers/gpu/drm/drm_edid_load.c
@@ -216,7 +216,8 @@ static void *edid_load(struct drm_connector *connector, const char *name,
goto out;
}

- if (!drm_edid_block_valid(edid, 0, print_bad_edid)) {
+ if (!drm_edid_block_valid(edid, 0, print_bad_edid,
+ &connector->edid_header_corrupt)) {
connector->bad_edid_counter++;
DRM_ERROR("Base block of EDID firmware \"%s\" is invalid ",
name);
@@ -229,7 +230,9 @@ static void *edid_load(struct drm_connector *connector, const char *name,
if (i != valid_extensions + 1)
memcpy(edid + (valid_extensions + 1) * EDID_LENGTH,
edid + i * EDID_LENGTH, EDID_LENGTH);
- if (drm_edid_block_valid(edid + i * EDID_LENGTH, i, print_bad_edid))
+ if (drm_edid_block_valid(edid + i * EDID_LENGTH, i,
+ print_bad_edid,
+ NULL))
valid_extensions++;
}

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index dae5c9a..9181483 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4005,6 +4005,7 @@ static uint8_t intel_dp_autotest_phy_pattern(struct intel_dp *intel_dp)

static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
{
+ struct drm_connector *connector = &intel_dp->attached_connector->base;
uint8_t response = DP_TEST_NAK;
uint8_t rxdata = 0;
int status = 0;
@@ -4051,6 +4052,9 @@ update_status:
&response, 1);
if (status <= 0)
DRM_DEBUG_KMS("Could not write test response to sink\n");
+
+ /* Clear EDID corruption flag now */
+ connector->edid_header_corrupt = 0;
}

static int
@@ -4135,7 +4139,7 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
* 4.2.2.1 - EDID read required for all HPD events
*/
edid_read = drm_get_edid(connector, adapter);
- if (!edid_read) {
+ if (!edid_read || connector->edid_header_corrupt == 1) {
DRM_DEBUG_DRIVER("Invalid EDID detected\n");
} else {
kfree(edid_read);
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index d4e4b82..f7a4a92 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -719,6 +719,11 @@ struct drm_connector {
int null_edid_counter; /* needed to workaround some HW bugs where we get all 0s */
unsigned bad_edid_counter;

+ /* Flag for raw EDID header corruption - used in Displayport
+ * compliance testing - * Displayport Link CTS Core 1.2 rev1.1 4.2.2.6
+ */
+ bool edid_header_corrupt;
+
struct dentry *debugfs_entry;

struct drm_connector_state *state;
@@ -1443,7 +1448,8 @@ extern void drm_set_preferred_mode(struct drm_connector *connector,
int hpref, int vpref);

extern int drm_edid_header_is_valid(const u8 *raw_edid);
-extern bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid);
+extern bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid,
+ bool *header_corrupt);
extern bool drm_edid_is_valid(struct edid *edid);

extern struct drm_tile_group *drm_mode_create_tile_group(struct drm_device *dev,