linux-kernel - Re: [PATCH 3/5] drm/msm/dpu: Check mode against PINGPONG or DSC max width

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Message-ID: <CAO9ioeVnbgWt8Ov0LF8y5dqydLM_7PhwHN3h=PEu-T2aibpkDA@mail.gmail.com>
Date: Fri, 16 May 2025 19:19:13 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Jessica Zhang <jessica.zhang@....qualcomm.com>
Cc: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Abhinav Kumar <abhinav.kumar@....qualcomm.com>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] drm/msm/dpu: Check mode against PINGPONG or DSC max width

On Fri, 16 May 2025 at 03:39, Jessica Zhang
<jessica.zhang@....qualcomm.com> wrote:
>
>
>
> On 5/14/2025 5:28 PM, Dmitry Baryshkov wrote:
> > On Wed, May 14, 2025 at 04:52:31PM -0700, Jessica Zhang wrote:
> >> Validate requested mode and topology based on the PINGPONG or DSC encoder
> >> max width. In addition, drop MAX_HDISPLAY_SPLIT and base LM reservation
> >> off of PINGPONG or DSC encoder max width
> >
> > Separate commit for num_lm, please.
>
> Hi Dmitry,
>
> Ack.
>
> >
> >>
> >> As noted in the patch, while DPU 8.x+ supports a max linewidth of 8960
> >> for PINGPONG_0, there is some additional logic that needs to be added to
> >> the resource manager to specifically try and reserve PINGPONG_0 for
> >> modes that are greater than 5k.
> >>
> >> Since this is out of the scope of this series, add a helper that will
> >> get the overall minimum PINGPONG max linewidth for a given chipset.
> >>
> >> Signed-off-by: Jessica Zhang <jessica.zhang@....qualcomm.com>
> >> ---
> >>   drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 46 +++++++++++++++++++++++++++-----
> >>   1 file changed, 39 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> >> index 0714936d8835..6131d071b051 100644
> >> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> >> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> >> @@ -723,6 +723,31 @@ void dpu_crtc_complete_commit(struct drm_crtc *crtc)
> >>      _dpu_crtc_complete_flip(crtc);
> >>   }
> >>
> >> +static int msm_display_get_max_pingpong_width(struct dpu_kms *dpu_kms)
> >> +{
> >> +    const struct dpu_pingpong_cfg *pingpong;
> >> +    u32 max_pingpong_width = dpu_kms->catalog->pingpong[0].max_linewidth;
> >> +
> >> +    /*
> >> +     * Find the smallest overall PINGPONG max_linewidth in the catalog since
> >> +     * max_linewidth can differ between PINGPONGs even within the same
> >> +     * chipset.
> >> +     *
> >> +     * Note: While, for DPU 8.x+, PINGPONG_0 can technically support up to
> >> +     * 8k resolutions, this requires reworking the RM to try to reserve
> >> +     * PINGPONG_0 for modes greater than 5k.
> >> +     *
> >> +     * Once this additional logic is implemented, we can drop this helper
> >> +     * and use the reserved PINGPONG's max_linewidth
> >> +     */
> >> +    for (int i = 1; i < dpu_kms->catalog->pingpong_count; i++) {
> >> +            pingpong = &dpu_kms->catalog->pingpong[i];
> >> +            max_pingpong_width = min(max_pingpong_width, pingpong->max_linewidth);
> >> +    }
> >
> > Since we are skipping PINGPONG_0, wouldn't it be enough to return
> > max_linewidth of PP_1 ?
>
> I don't think we're skipping PINGPONG_0 here since `u32
> max_pingpong_width = dpu_kms->catalog->pingpong[0].max_linewidth;` at
> the top of the function.
>
> >
> > I think, it would be easier to follow .max_dsc_encoder_width and store
> > .max_pingpong_linewidth in dpu_caps (and later add special
> > .max_pp0_linewidth).
>
> Ack. I think my only concern for this is that max_pp0_linewidth won't be
> set for all chipsets. But if you're fine with that I'll go ahead and
> make this change.

You can set it for all chipsets having PINGPONG_0. It might be the
same as .max_pingpong_linewidth, but that's not a problem.

>
> Thanks,
>
> Jessica Zhang
>
> >
> >> +
> >> +    return max_pingpong_width;
> >> +}
> >> +
> >>   static int _dpu_crtc_check_and_setup_lm_bounds(struct drm_crtc *crtc,
> >>              struct drm_crtc_state *state)
> >>   {
> >
>

--
With best wishes
Dmitry