[06/11] drm/i915: Add supporting structure for Displayport Link CTS test 4.2.2.6

Submitted by Todd Previte on April 10, 2015, 4:12 p.m.

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Message ID 1428682372-21586-7-git-send-email-tprevite@gmail.com
State New
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Commit Message

Todd Previte April 10, 2015, 4:12 p.m.
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

Signed-off-by: Todd Previte <tprevite@gmail.com>
Cc: dri-devel@lists.freedesktop.org
---
 drivers/gpu/drm/drm_edid.c        | 31 ++++++++++++++++++++++++++-----
 drivers/gpu/drm/drm_edid_load.c   |  7 +++++--
 drivers/gpu/drm/i2c/tda998x_drv.c |  4 ++--
 include/drm/drm_crtc.h            |  8 +++++++-
 4 files changed, 40 insertions(+), 10 deletions(-)

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 53bc7a6..12e5be7 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1005,7 +1005,6 @@  int drm_edid_header_is_valid(const u8 *raw_edid)
 	for (i = 0; i < sizeof(edid_header); i++)
 		if (raw_edid[i] == edid_header[i])
 			score++;
-
 	return score;
 }
 EXPORT_SYMBOL(drm_edid_header_is_valid);
@@ -1047,7 +1046,8 @@  static bool drm_edid_is_zero(const u8 *in_edid, int length)
  *
  * 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 +1062,27 @@  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 then correct
+			 * and the test fails
+			 */
+			csum = drm_edid_block_checksum(raw_edid);
+			if (csum) {
+				DRM_DEBUG_DRIVER("Invalid EDID header, score = %d\n", score);
+				DRM_DEBUG_DRIVER("Invalid EDID checksum %d\n", 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 +1276,9 @@  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,
+						 &connector->edid_header_corrupt)) {
 				valid_extensions++;
 				break;
 			}
diff --git a/drivers/gpu/drm/drm_edid_load.c b/drivers/gpu/drm/drm_edid_load.c
index 732cb6f..1505494 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,
+					 &connector->edid_header_corrupt))
 			valid_extensions++;
 	}
 
diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
index a9041d1..9c3d6b3 100644
--- a/drivers/gpu/drm/i2c/tda998x_drv.c
+++ b/drivers/gpu/drm/i2c/tda998x_drv.c
@@ -1106,7 +1106,7 @@  static uint8_t *do_get_edid(struct tda998x_priv *priv)
 	if (read_edid_block(priv, block, 0))
 		goto fail;
 
-	if (!drm_edid_block_valid(block, 0, print_bad_edid))
+	if (!drm_edid_block_valid(block, 0, print_bad_edid, NULL))
 		goto fail;
 
 	/* if there's no extensions, we're done */
@@ -1123,7 +1123,7 @@  static uint8_t *do_get_edid(struct tda998x_priv *priv)
 		if (read_edid_block(priv, ext_block, j))
 			goto fail;
 
-		if (!drm_edid_block_valid(ext_block, j, print_bad_edid))
+		if (!drm_edid_block_valid(ext_block, j, print_bad_edid, NULL))
 			goto fail;
 
 		valid_extensions++;
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 0261417..e31a4b3 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;
@@ -1436,7 +1441,8 @@  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,

Comments

Easy enough to do. Tag removed and updated patch posted. Thanks Emil!

On 4/10/2015 10:45 AM, Emil Velikov wrote:
> Hi Todd
>
> On 10/04/15 16:12, Todd Previte wrote:
>> 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
>>
>> Signed-off-by: Todd Previte <tprevite@gmail.com>
>> Cc: dri-devel@lists.freedesktop.org
>> ---
>>   drivers/gpu/drm/drm_edid.c        | 31 ++++++++++++++++++++++++++-----
>>   drivers/gpu/drm/drm_edid_load.c   |  7 +++++--
>>   drivers/gpu/drm/i2c/tda998x_drv.c |  4 ++--
>>   include/drm/drm_crtc.h            |  8 +++++++-
>>   4 files changed, 40 insertions(+), 10 deletions(-)
>>
> Neither this nor patch 09/11 seems to be i915 specific. If you're doing
> another revision you might want to use just "drm:".
>
> Cheers,
> Emil
Hi Todd

On 10/04/15 16:12, Todd Previte wrote:
> 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
> 
> Signed-off-by: Todd Previte <tprevite@gmail.com>
> Cc: dri-devel@lists.freedesktop.org
> ---
>  drivers/gpu/drm/drm_edid.c        | 31 ++++++++++++++++++++++++++-----
>  drivers/gpu/drm/drm_edid_load.c   |  7 +++++--
>  drivers/gpu/drm/i2c/tda998x_drv.c |  4 ++--
>  include/drm/drm_crtc.h            |  8 +++++++-
>  4 files changed, 40 insertions(+), 10 deletions(-)
> 
Neither this nor patch 09/11 seems to be i915 specific. If you're doing
another revision you might want to use just "drm:".

Cheers,
Emil