On Wed, Mar 17, 2021 at 08:49:01PM +0200, Imre Deak wrote:
> By the specification the 0xF0000 - 0xF02FF range is only valid if the
> LTTPR revision at 0xF0000 is at least 1.4. Disable the LTTPR support
> otherwise.
>
> Fixes: 7b2a4ab8b0ef ("drm/i915: Switch to LTTPR transparent mode link training")
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.11
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
> ---
> .../gpu/drm/i915/display/intel_dp_link_training.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> index d8d90903226f..d92eb192c89d 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -100,17 +100,23 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp)
> return false;
>
> if (drm_dp_read_lttpr_common_caps(&intel_dp->aux,
> - intel_dp->lttpr_common_caps) < 0) {
> - intel_dp_reset_lttpr_common_caps(intel_dp);
> - return false;
> - }
> + intel_dp->lttpr_common_caps) < 0)
> + goto reset_caps;
BTW just noticed this oddball thing in the spec:
"DPTX shall read specific registers within the LTTPR field (DPCD
Addresses F0000h through F0004h; see Table 2-198) to determine
whether any LTTPR(s) are present and if so, how many. This read
shall be in the form of a 5-byte native AUX Read transaction."
Why exactly 5 bytes? I have no idea. Doesn't really make sense.
Just wondering if we really need to respect that and some LTTPRs
would fsck things up if we read more...
Anyways
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
> "LTTPR common capabilities: %*ph\n",
> (int)sizeof(intel_dp->lttpr_common_caps),
> intel_dp->lttpr_common_caps);
>
> + /* The minimum value of LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV is 1.4 */
> + if (intel_dp->lttpr_common_caps[0] < 0x14)
> + goto reset_caps;
> +
> return true;
> +
> +reset_caps:
> + intel_dp_reset_lttpr_common_caps(intel_dp);
> + return false;
> }
>
> static bool
> --
> 2.25.1
--
Ville Syrjälä
Intel
