Re: [PATCH 05/12] drm: Add supporting structure for Displayport Link CTS test 4.2.2.6

Todd Previte
2015-04-16T14:02:10Z

On 4/16/2015 6:34 AM, Paulo Zanoni wrote:
> 2015-04-15 19:03 GMT-03:00 Todd Previte <tprevite@gmail.com>:
>> 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
>> V7:
>> - Updated to account for long_pulse flag propagation
>> V8:
>> - Removed clearing of header_corrupt flag from the test handler in intel_dp.c
>> - Added clearing of header_corrupt flag in the drm_edid_block_valid function
>>
>> Signed-off-by: Todd Previte <tprevite@gmail.com>
>> Cc: dri-devel@lists.freedesktop.org
>> ---
>> drivers/gpu/drm/drm_edid.c | 35 +++++++++++++++++++++++++++++------
>> drivers/gpu/drm/drm_edid_load.c | 7 +++++--
>> drivers/gpu/drm/i915/intel_dp.c | 2 +-
>> include/drm/drm_crtc.h | 8 +++++++-
>> 4 files changed, 42 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>> index 53bc7a6..6d037f9 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;
>> @@ -1060,11 +1062,28 @@ bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid)
>>
>> if (block == 0) {
>> int score = drm_edid_header_is_valid(raw_edid);
>> - if (score == 8) ;
>> - else if (score >= edid_fixup) {
>> + if (score == 8) {
>> + if (header_corrupt)
>> + *header_corrupt = 0;
>> + } 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;
>> + }
>
> I was ready to give the R-B tag, but then I realized this. Shouldn't
> we be setting header_corrupt here regardless of the checksum value? I
> mean, score is not 8, so the header is indeed corrupt.
I added the checksum computation as an extra validation that the header
was indeed corrupt. However, that checksum is discarded so the
additional checksum generation isn't strictly necessary. I've removed it
in the updated patch.
> Also, setting "header_corrupt" to 1 in case the checksum is invalid is
> somewhat a distortion of meaning in the variable. If we really need
> the checksum, we should probably have something like
> connector->raw_checksum, or maybe rename header_corrupt to
> edid_corrupt, where "edid_corrupt" means "either invalid header or
> invalid checksum"?
I was thinking the same thing as I've been working with this. I think
renaming it to "edid_corrupt" is more accurate. Fixed in the update.
> And for compliance testing specifically, as far as I understand, I see
> on patch 7 that you only care about the checksum if the header is
> valid, so we don't seem to need the csum value here, so it seems my
> suggestion to just assign header_corrupt=1 regardless of the checksum
> value seems to be enough to solve your problem.
Agreed.
> Sorry for not realizing this earlier, the back-and-forth between
> patches royally confused me.
Indeed, that's an issue for me as well.
>
>> DRM_DEBUG("Fixing EDID header, your hardware may be failing\n");
>> memcpy(raw_edid, edid_header, sizeof(edid_header));
>> } else {
>> + if (header_corrupt) {
>> + *header_corrupt = 1;
>> + }
>> goto bad;
>> }
>> }
>> @@ -1129,7 +1148,7 @@ 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 +1251,8 @@ 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 +1277,10 @@ 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 7ca0e18..97224ff 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -4139,7 +4139,7 @@ intel_dp_check_link_status(struct intel_dp *intel_dp, bool long_hpd)
>> */
>> if (long_hpd) {
>> 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,
>> --
>> 1.9.1
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>
>

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