Re: [PATCH 3/4] drm/msm/dp: skip LTTPR init when no LTTPRs are present

[Dmitry Baryshkov]

On Mon, Sep 07, 2026 at 03:14:33PM +0530, Saurabh Anand wrote:
> 
> On 24-08-2026 18:45, Konrad Dybcio wrote:
> > On 8/24/26 1:28 PM, Saurabh Anand wrote:
> > > drm_dp_lttpr_count() returns 0 when no LTTPRs are detected and a
> > > negative value on error. The previous code passed the result directly
> > > to drm_dp_lttpr_init() without checking, which would call into the
> > > LTTPR transparency-mode setup with a zero or negative repeater count.
> > > 
> > > Add an early return for lttpr_count <= 0 to skip the init entirely
> > > when there are no repeaters in the link, matching the expected usage
> > > of drm_dp_lttpr_init().
> > Reading the body of that function, I'm not sure your statement is true
> 
> drm_dp_lttpr_count() returns 0 when no LTTPRs are detected and a
> negative error code when the LTTPR common capabilities report an invalid
> or unsupported repeater count.
> 
> drm_dp_lttpr_init() already handles the zero-count case by returning
> early. However, when passed a negative count, it still writes transparent
> mode before returning -ENODEV.

And this is correct. If there are more than 8 LTTPRs, they must be
switched to the transparent mode as it's impossible to control them
individually.

> 
> I will update the commit message giving more details.
> 
> > 
> > Konrad

-- 
With best wishes
Dmitry