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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 14 Jun 2022, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> On Tue, 14 Jun 2022, Imre Deak <imre.deak@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.

Oh,

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

on the changes, I'm just wondering about the statement in the commit
message.



>
> 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@redhat.com>
>> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5292
>> Signed-off-by: Imre Deak <imre.deak@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