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

[Lyude Paul]

If you add a Cc: to stable at vger.kernel.org then this is:

Reviewed-by: Lyude Paul <lyude at redhat.com>

I assume you have the privileges to push this to drm-misc-next

On Tue, 2022-06-14 at 12:45 +0300, Imre Deak 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.
> 
> 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;
>                 }

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat