Re: [PATCH v4 18/39] drm/msm/dp: add support to send ACT packets for MST

[Dmitry Baryshkov]

On Mon, Jun 15, 2026 at 04:21:14PM +0800, Yongxing Mou wrote:
> 
> 
> On 4/12/2026 2:57 AM, Dmitry Baryshkov wrote:
> > On Fri, Apr 10, 2026 at 05:33:53PM +0800, Yongxing Mou wrote:
> > > From: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > > 
> > > 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.
> > > 
> > > Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > > Signed-off-by: Yongxing Mou <yongxing.mou@xxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/msm/dp/dp_ctrl.c    | 43 +++++++++++++++++++++++++++++++++++--
> > >   drivers/gpu/drm/msm/dp/dp_ctrl.h    |  3 ++-
> > >   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     |  2 ++
> > >   5 files changed, 48 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > > index 1109b2df21be..6f25145ef214 100644
> > > --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > > +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > > @@ -143,6 +143,7 @@ struct msm_dp_ctrl_private {
> > >   	bool core_clks_on;
> > >   	bool link_clks_on;
> > >   	bool stream_clks_on[DP_STREAM_MAX];
> > > +	bool mst_active;
> > >   };
> > >   static inline u32 msm_dp_read_ahb(const struct msm_dp_ctrl_private *ctrl, u32 offset)
> > > @@ -228,6 +229,32 @@ static int msm_dp_aux_link_configure(struct drm_dp_aux *aux,
> > >   	return err;
> > >   }
> > > +int msm_dp_ctrl_mst_send_act(struct msm_dp_ctrl *msm_dp_ctrl)
> > > +{
> > > +	struct msm_dp_ctrl_private *ctrl;
> > > +	bool act_complete;
> > > +
> > > +	ctrl = container_of(msm_dp_ctrl, struct msm_dp_ctrl_private, msm_dp_ctrl);
> > > +
> > > +	if (!ctrl->mst_active)
> > > +		return 0;
> > > +
> > > +	msm_dp_write_link(ctrl, 0, REG_DP_MST_ACT, 0x1);
> > > +	/* make sure ACT signal is performed */
> > > +	wmb();
> > > +
> > > +	msleep(20); /* needs 1 frame time */
> > 
> > 20 ms is 50fps. What if we have 30 or 25 fps?
> > 
> This hasn’t been considered yet. Do we need to change this to wait based on
> the per-frame duration of the mode?

I don't know. You wrote that we wait for 1 frame here. Why?


-- 
With best wishes
Dmitry