On Thu, Jul 19, 2018 at 01:35:49PM -0700, matthew.s.atwood@xxxxxxxxx wrote:
> From: Matt Atwood <matthew.s.atwood@xxxxxxxxx>
>
> According to DP spec (2.9.3.1 of DP 1.4) if
> EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT is set the addresses in DPCD
> 02200h through 0220Fh shall contain the DPRX's true capability. These
> values will match 00000h through 0000Fh, except for DPCD_REV,
> MAX_LINK_RATE, DOWN_STREAM_PORT_PRESENT.
>
> Read from DPCD once for all 3 values as this is an expensive operation.
> Spec mentions that all of address space 02200h through 0220Fh should
> contain the right information however currently only 3 values can
> differ.
>
> There is no address space in the intel_dp->dpcd struct for addresses
> 02200h through 0220Fh, and since so much of the data is a identical,
> simply overwrite the values stored in 00000h through 0000Fh with the
> values that can be overwritten from addresses 02200h through 0220Fh.
>
> This patch helps with backward compatibility for devices pre DP1.3.
>
> v2: read only dpcd values which can be affected, remove incorrect check,
> split into drm include changes into separate patch, commit message,
> verbose debugging statements during overwrite.
>
> v3: white space fixes
>
> Signed-off-by: Matt Atwood <matthew.s.atwood@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 37 +++++++++++++++++++++++++++++++++
> 1 file changed, 37 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index dde92e4af5d3..a31fbbbd7954 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3738,6 +3738,43 @@ intel_dp_read_dpcd(struct intel_dp *intel_dp)
> sizeof(intel_dp->dpcd)) < 0)
> return false; /* aux transfer failed */
>
We never know what vendors can do with reserved bits. We should never assume
they are zero. So we shouldn't do any of below unless it is newer than DP 1.3.
> + if (intel_dp->dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> + DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT) {
> + uint8_t dpcd_ext[6];
> +
> + DRM_DEBUG_KMS("DPCD: Extended Receiver Capability Field Present, accessing 02200h through 022FFh\n");
> +
> + if (drm_dp_dpcd_read(&intel_dp->aux, DP_DP13_DPCD_REV,
> + &dpcd_ext, sizeof(dpcd_ext)) < 0)
> + return false; /* aux transfer failed */
> +
> + if (memcmp(&intel_dp->dpcd[DP_DPCD_REV], &dpcd_ext[DP_DPCD_REV],
> + sizeof(u8))) {
> + DRM_DEBUG_KMS("DPCD: new value for DPCD Revision previous value %2x new value %2x\n",
> + intel_dp->dpcd[DP_DPCD_REV],
> + dpcd_ext[DP_DPCD_REV]);
> + memcpy(&intel_dp->dpcd[DP_DPCD_REV],
> + &dpcd_ext[DP_DPCD_REV],
> + sizeof(u8));
> + }
> + if (memcmp(&intel_dp->dpcd[DP_MAX_LINK_RATE],
> + &dpcd_ext[DP_MAX_LINK_RATE], sizeof(u8))) {
> + DRM_DEBUG_KMS("DPCD: new value for DPCD Max Link Rate previous value %2x new value %2x\n",
> + intel_dp->dpcd[DP_MAX_LINK_RATE],
> + dpcd_ext[DP_MAX_LINK_RATE]);
> + memcpy(&intel_dp->dpcd[DP_MAX_LINK_RATE],
> + &dpcd_ext[DP_MAX_LINK_RATE], sizeof(u8));
> + }
> + if (memcmp(&intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT],
> + &dpcd_ext[DP_DOWNSTREAMPORT_PRESENT], sizeof(u8))) {
> + DRM_DEBUG_KMS("DPCD: new value for DPCD Downstream Port Present previous value %2x new value %2x\n",
> + intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT],
> + dpcd_ext[DP_DOWNSTREAMPORT_PRESENT]);
> + memcpy(&intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT],
> + &dpcd_ext[DP_DOWNSTREAMPORT_PRESENT],
> + sizeof(u8));
> + }
> + }
> DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
>
> return intel_dp->dpcd[DP_DPCD_REV] != 0;
> --
> 2.17.1
>
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