Re: [PATCH v4 14/39] drm/msm/dp: introduce max_streams for DP controller MST support

[Yongxing Mou]

On 4/12/2026 1:59 AM, Dmitry Baryshkov wrote:
> On Fri, Apr 10, 2026 at 05:33:49PM +0800, Yongxing Mou wrote:
> > From: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> >
> > Introduce the `mst_streams` field in each DP controller descriptor to
> > specify the number of supported MST streams. Most platforms support 2 or
> > 4 MST streams, while platforms without MST support default to a single
> > stream (`DEFAULT_STREAM_COUNT = 1`).
>
> There is no such const anymore.
>
> > Also accounts for platforms with asymmetric stream support, e.g., DP0
> > supporting 4 streams and DP1 supporting 2.
>
> There is no need to mention it.
>
> > Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > Signed-off-by: Yongxing Mou <yongxing.mou@xxxxxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/dp/dp_ctrl.c    | 20 +++++++++++++++++---
> >   drivers/gpu/drm/msm/dp/dp_ctrl.h    |  2 ++
> >   drivers/gpu/drm/msm/dp/dp_display.c | 20 +++++++++++++++++++-
> >   drivers/gpu/drm/msm/dp/dp_display.h |  1 +
> >   4 files changed, 39 insertions(+), 4 deletions(-)
> >
> > @@ -2740,7 +2741,8 @@ static int msm_dp_ctrl_clk_init(struct msm_dp_ctrl *msm_dp_ctrl)
> >   	if (rc)
> >   		return rc;
> >   
> > -	for (i = DP_STREAM_0; i < DP_STREAM_MAX; i++) {
> > +	ctrl->num_pixel_clks = 0;
> > +	for (i = DP_STREAM_0; i < max_stream; i++) {
>
> Why? I think the code was fine with getting up to DP_STREAM_MAX clocks.
Sure.. will change max_stream -> DP_STREAM_MAX next version.
> In fact, I'd rather use that instead of the hardcoded value for
> determining how many streams can be there. Think of the old DTs which
> didn't have extra stream clocks. We still need to support those.
The current logic only assigns num streams to dp->max_stream when 
desc->mst_streams == num_pixel_clks, otherwise set to 1 which mean sst.
I would like to introduce a switch in the driver to control the number 
of streams, rather than having it fully determined by the DTs.
Do you think it would be acceptable to use:
dp->max_stream = min(num_pixel_clks, desc->mst_streams)?

> >   		ctrl->pixel_clk[i] = devm_clk_get(dev, pixel_clks[i]);
> >   
> >   		if (i == 0 && IS_ERR(ctrl->pixel_clk[i]))
> > @@ -2750,14 +2752,26 @@ static int msm_dp_ctrl_clk_init(struct msm_dp_ctrl *msm_dp_ctrl)
> >   			DRM_DEBUG_DP("stream %d pixel clock not exist", i);
> >   			break;
> >   		}
> > +
> > +		ctrl->num_pixel_clks++;
> >   	}
> >   
> >   	return 0;
> >   }
> >   
> > @@ -1234,6 +1248,10 @@ static int msm_dp_display_probe(struct platform_device *pdev)
> >   	dp->msm_dp_display.is_edp =
> >   		(dp->msm_dp_display.connector_type == DRM_MODE_CONNECTOR_eDP);
> >   	dp->hpd_isr_status = 0;
> > +	dp->max_stream = 1;
> > +
> > +	if (desc->mst_streams > 1)
> > +		dp->max_stream = desc->mst_streams;
>
> Here you can assign it from the DT resources.
>
> >   
> >   	mutex_init(&dp->plugged_lock);
> >   
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.h b/drivers/gpu/drm/msm/dp/dp_display.h
> > index a5c6ed5b18e4..b0cfdf215970 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.h
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.h
> > @@ -26,6 +26,7 @@ struct msm_dp {
> >   	bool psr_supported;
> >   };
> >   
> > +int msm_dp_get_mst_max_stream(struct msm_dp *msm_dp_display);
> >   int msm_dp_display_get_modes(struct msm_dp *msm_dp_display);
> >   bool msm_dp_display_check_video_test(struct msm_dp *msm_dp_display);
> >   int msm_dp_display_get_test_bpp(struct msm_dp *msm_dp_display);
> >
> > --
> > 2.43.0