2015-04-13 11:53 GMT-03:00 Todd Previte <tprevite@xxxxxxxxx>:
> 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
>
> Signed-off-by: Todd Previte <tprevite@xxxxxxxxx>
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> ---
> drivers/gpu/drm/drm_edid.c | 31 ++++++++++++++++++++++++++-----
> drivers/gpu/drm/drm_edid_load.c | 7 +++++--
> drivers/gpu/drm/i2c/tda998x_drv.c | 4 ++--
> drivers/gpu/drm/i915/intel_dp.c | 2 +-
> include/drm/drm_crtc.h | 8 +++++++-
> 5 files changed, 41 insertions(+), 11 deletions(-)
>
> 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);
Bad chunk...
> @@ -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)
Need to add the new parameter description to the documentation above.
> {
> 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);
No one on this file uses DRM_DEBUG_DRIVER (you use 2 calls here and one below).
Also, during "normal operation" we try to calculate the checksum based
on the fixed EDID header, so if we also print these messages here
we're always going to have a message complaining about invalid
checksum: either this one or the other that's already there. My
bikeshed would be to just remove the messages you added here and below
to not confuse users. Let's assume that the bad header is due to some
communication/corruption error, and the HW manufacturers did not
program an EDID with a bad header and a correct checksum based on bad
header :)
> + 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;
> + }
We don't ever set header_corrupt back to false, so if we ever get a
corrupt header once, the header_corrupt flag will stay there even if
it gets fixed somehow (such as a DP compliance tester starting to
submit the correct header).
> 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)) {
You can use NULL here since we're not handling block 0 anymore.
> 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))
Same here: not iterating over block 0.
Btw, why can't we just use NULL on edid_load?
> 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/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index e1d6e79..77b6b15 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3922,7 +3922,7 @@ 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");
> }
>
> 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,
> --
> 1.9.1
>
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> dri-devel@xxxxxxxxxxxxxxxxxxxxx
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Paulo Zanoni
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