Re: [PATCH v7 08/35] drm/msm/dp: add support to send ACT packets for MST

[Yongxing Mou <yongxing.mou@oss.qualcomm.com>]

On 10/1/2026 6:32 PM, Dmitry Baryshkov wrote:
> On Tue, Sep 29, 2026 at 12:25:32PM +0800, Yongxing Mou wrote:
>> From: Abhinav Kumar <quic_abhinavk@quicinc.com>
>>
>> Whenever virtual channel slot allocation changes, the DP
>> source must send the action control trigger sequence to notify
>> the sink about the same. This would be applicable during the
>> start and stop of the pixel stream. Add the infrastructure
>> to be able to send ACT packets for the DP controller when
>> operating in MST mode.
>>
>> Add REG_DP_MST_ACT, the ACT trigger register used by this sequence.
>>
>> Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
>> Signed-off-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
>> ---
>>   drivers/gpu/drm/msm/dp/dp_ctrl.c    | 44 ++++++++++++++++++++++++++++++++++++-
>>   drivers/gpu/drm/msm/dp/dp_ctrl.h    |  5 ++++-
>>   drivers/gpu/drm/msm/dp/dp_display.c |  3 ++-
>>   drivers/gpu/drm/msm/dp/dp_display.h |  1 +
>>   drivers/gpu/drm/msm/dp/dp_reg.h     |  1 +
>>   5 files changed, 51 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> index e1614bc49a7c..65d22505c2b6 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> @@ -142,6 +142,7 @@ struct msm_dp_ctrl_private {
>>   	bool core_clks_on;
>>   	bool link_clks_on;
>>   	bool stream_clks_on[DP_STREAM_MAX];
>> +	bool mst_active;
> 
> I really don't like the idea of having this flag in two locations. Here
> and in the msm_dp_display_private. Can we have it in one place only?
> 
These two fields are intended to represent different states with 
different lifetimes.

msm_dp::mst_active tracks whether the DP connection has an active MST 
session. The controller field records whether the current 
controller/link is operating in MST mode and remains valid until the 
link is shut down.

I agree that using mst_active for both fields makes them look like 
duplicated state. I propose renaming the controller field to mst_mode 
while keeping the display-side field as mst_active.

Would you agree with this change?
>>   };
>>   
> 
> [...]
> 
>>   
>>   static void msm_dp_display_unprepare(struct msm_dp_display_private *dp)
>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.h b/drivers/gpu/drm/msm/dp/dp_display.h
>> index 83117e7619f3..472429d09200 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_display.h
>> +++ b/drivers/gpu/drm/msm/dp/dp_display.h
>> @@ -19,6 +19,7 @@ struct msm_dp {
>>   	struct drm_bridge *bridge;
>>   	bool audio_enabled;
>>   	bool power_on;
>> +	bool mst_active;
>>   	unsigned int connector_type;
>>   	bool is_edp;
>>   
>