Re: [PATCH v3 12/38] drm/msm/dp: introduce max_streams for DP controller MST support

[Dmitry Baryshkov]

On Mon, Mar 30, 2026 at 05:59:28PM +0800, Yongxing Mou wrote:
> 
> 
> On 9/2/2025 5:41 PM, Dmitry Baryshkov wrote:
> > On Mon, Aug 25, 2025 at 10:15:58PM +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`).
> > > 
> > > This change also accounts for platforms with asymmetric stream support,
> > > e.g., DP0 supporting 4 streams and DP1 supporting 2.
> > > 
> > > Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > > Signed-off-by: Yongxing Mou <yongxing.mou@xxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/msm/dp/dp_display.c | 21 +++++++++++++++++++++
> > >   drivers/gpu/drm/msm/dp/dp_display.h |  1 +
> > >   2 files changed, 22 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > > index 78d932bceb581ee54116926506b1025bd159108f..a8477a0a180137f15cbb1401c3964636aa32626c 100644
> > > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > > @@ -33,6 +33,7 @@ module_param(psr_enabled, bool, 0);
> > >   MODULE_PARM_DESC(psr_enabled, "enable PSR for eDP and DP displays");
> > >   #define HPD_STRING_SIZE 30
> > > +#define DEFAULT_STREAM_COUNT 1
> > >   enum {
> > >   	ISR_DISCONNECTED,
> > > @@ -52,6 +53,7 @@ struct msm_dp_display_private {
> > >   	bool core_initialized;
> > >   	bool phy_initialized;
> > >   	bool audio_supported;
> > > +	bool mst_supported;
> > >   	struct drm_device *drm_dev;
> > > @@ -84,12 +86,15 @@ struct msm_dp_display_private {
> > >   	void __iomem *p0_base;
> > >   	size_t p0_len;
> > > +
> > > +	int max_stream;
> > >   };
> > >   struct msm_dp_desc {
> > >   	phys_addr_t io_start;
> > >   	unsigned int id;
> > >   	bool wide_bus_supported;
> > > +	int mst_streams;
> > >   };
> > >   static const struct msm_dp_desc msm_dp_desc_sa8775p[] = {
> > > @@ -1213,6 +1218,15 @@ static int msm_dp_display_get_io(struct msm_dp_display_private *display)
> > >   	return 0;
> > >   }
> > > +int msm_dp_get_mst_max_stream(struct msm_dp *msm_dp_display)
> > > +{
> > > +	struct msm_dp_display_private *dp;
> > > +
> > > +	dp = container_of(msm_dp_display, struct msm_dp_display_private, msm_dp_display);
> > > +
> > > +	return dp->max_stream;
> > > +}
> > > +
> > >   static int msm_dp_display_probe(struct platform_device *pdev)
> > >   {
> > >   	int rc = 0;
> > > @@ -1239,6 +1253,13 @@ 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 = DEFAULT_STREAM_COUNT;
> > > +	dp->mst_supported = FALSE;
> > > +
> > > +	if (desc->mst_streams > DEFAULT_STREAM_COUNT) {
> > > +		dp->max_stream = desc->mst_streams;
> > 
> > We should keep compatibility with earlier DT files which didn't define
> > enough stream clocks for DP MST case. Please check how many stream
> > clocks are actually present in the DT and set max_stream accordingly.
> > 
> Now these DTs should already have the MST clocks added.

I wrote a different phrase: we need to keep compatibility with _earlier_
DTs. It's called an ABI.

> > > +		dp->mst_supported = TRUE;
> > > +	}
> > >   	rc = msm_dp_display_get_io(dp);
> > >   	if (rc)
> > > diff --git a/drivers/gpu/drm/msm/dp/dp_display.h b/drivers/gpu/drm/msm/dp/dp_display.h
> > > index 37c6e87db90ce951274cdae61f26d76dc9ef3840..7727cf325a89b4892d2370a5616c4fa76fc88485 100644
> > > --- a/drivers/gpu/drm/msm/dp/dp_display.h
> > > +++ b/drivers/gpu/drm/msm/dp/dp_display.h
> > > @@ -29,6 +29,7 @@ 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);
> > > 
> > > -- 
> > > 2.34.1
> > > 
> > 
> 

-- 
With best wishes
Dmitry