[Intel-gfx] [PATCH] drm/dp/mst: Read the extended DPCD capabilities during system resume

[Jani Nikula]

On Tue, 14 Jun 2022, Imre Deak <imre.deak at intel.com> wrote:
> The WD22TB4 Thunderbolt dock at least will revert its DP_MAX_LINK_RATE
> from HBR3 to HBR2 after system suspend/resume if the DP_DP13_DPCD_REV
> registers are not read subsequently also as required.

Does it actually change the behaviour depending on whether the dpcd is
read or not, or is this just about the resume path overwriting mgr->dpcd
with stuff from DP_DPCD_REV?

drm_dp_mst_topology_mgr_set_mst() does use drm_dp_read_dpcd_caps() for
reading the caps, which would normally set mgr->dpcd from
DP_DP13_DPCD_REV.

BR,
Jani.

>
> Fix this by reading DP_DP13_DPCD_REV registers as well, matching what is
> done during connector detection. While at it also fix up the same call
> in drm_dp_mst_dump_topology().
>
> Cc: Lyude Paul <lyude at redhat.com>
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5292
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/display/drm_dp_mst_topology.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> index 67b3b9697da7f..18f2b6075b780 100644
> --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> @@ -3860,9 +3860,7 @@ int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr,
>  	if (!mgr->mst_primary)
>  		goto out_fail;
>  
> -	ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, mgr->dpcd,
> -			       DP_RECEIVER_CAP_SIZE);
> -	if (ret != DP_RECEIVER_CAP_SIZE) {
> +	if (drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd) < 0) {
>  		drm_dbg_kms(mgr->dev, "dpcd read failed - undocked during suspend?\n");
>  		goto out_fail;
>  	}
> @@ -4911,8 +4909,7 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
>  		u8 buf[DP_PAYLOAD_TABLE_SIZE];
>  		int ret;
>  
> -		ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, buf, DP_RECEIVER_CAP_SIZE);
> -		if (ret) {
> +		if (drm_dp_read_dpcd_caps(mgr->aux, buf) < 0) {
>  			seq_printf(m, "dpcd read failed\n");
>  			goto out;
>  		}

-- 
Jani Nikula, Intel Open Source Graphics Center