Re: [PATCH 1/3] drm/i915: Displayport compliance test 4.2.2.9 support

Daniel Vetter
2015-06-15T15:35:13Z

On Tue, Jun 09, 2015 at 05:22:18PM -0700, Todd Previte wrote:
> Implement the fix for test 4.2.2.9. This test is a 4-block E-DDC
> read over the AUX channel. For test purposes, the normal 1-block
> EDID read is required to write the checksum of that block to the
> sink device via the AUX channel. For 4.2.2.9, that checksum must
> be the checksum of the last block read. The DRM EDID read code
> already does the 4-block read, so the checksum just needs to be
> adjusted to the one that we need based on the number of extensions
> detected in the block.
>
> Signed-off-by: Todd Previte <tprevite@gmail.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index c7cbb67..14147d0 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4020,9 +4020,17 @@ static uint8_t intel_dp_autotest_edid(struct intel_dp *intel_dp)
> intel_dp->aux.i2c_defer_count);
> intel_dp->compliance_test_data = INTEL_DP_RESOLUTION_FAILSAFE;
> } else {
> + /* Checksum write for EDID reads (DP CTS 1.2 Core r1.1)
> + * 4.2.2.3: checksum of EDID block 0
> + * 4.2.2.9: checksum of the last 128-byte block read
> + */
> + int checksum = *(&intel_connector->detect_edid->checksum +
> + (intel_connector->detect_edid->extensions *
> + EDID_LENGTH));
> +
> if (!drm_dp_dpcd_write(&intel_dp->aux,
> DP_TEST_EDID_CHECKSUM,
> - &intel_connector->detect_edid->checksum,
> + &checksum,

This is some pretty hairy pointer arithmetic. I think it'd be good to have
a little dp helper function which takes the edid and dp aux pointer and
sends the right checksum to the right dp aux register. Then we could move
the above comment into kerneldoc code.
-Daniel

> 1))
> DRM_DEBUG_KMS("Failed to write EDID checksum\n");
>
> --
> 1.9.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

--
Daniel Vetter
Software Engineer, Intel Corporation