linux-kernel - Re: [v1] drm/msm/dpu: consider vertical front porch in the prefill bw calculation

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Date:   Wed, 25 Nov 2020 16:54:13 +0530
From:   Amit Pundir <amit.pundir@...aro.org>
To:     Kalyan Thota <kalyan_t@...eaurora.org>
Cc:     y@...lcomm.com, dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        dt <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Rob Clark <robdclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        "Kristian H. Kristensen" <hoegsberg@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Krishna Manikandan <mkrishn@...eaurora.org>,
        Raviteja Tamatam <travitej@...eaurora.org>,
        nganji@...eaurora.org, Stephen Boyd <swboyd@...omium.org>,
        abhinavk@...eaurora.org, ddavenport@...omium.org,
        Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [v1] drm/msm/dpu: consider vertical front porch in the prefill bw calculation

On Wed, 25 Nov 2020 at 15:33, Kalyan Thota <kalyan_t@...eaurora.org> wrote:
>
> In case of panels with low vertical back porch, the prefill bw
> requirement will be high as we will have less time(vbp+pw) to
> fetch and fill the hw latency buffers before start of first line
> in active period.
>
> For ex:
> Say hw_latency_line_buffers = 24, and if blanking vbp+pw = 10
> Here we need to fetch 24 lines of data in 10 line times.
> This will increase the bw to the ratio of linebuffers to blanking.
>
> DPU hw can also fetch data during vertical front porch provided
> interface prefetch is enabled. Use vfp in the prefill calculation
> as dpu driver enables prefetch if the blanking is not sufficient
> to fill the latency lines.

Tested on Xiaomi Poco F1 (sdm845).

Tested-by: Amit Pundir <amit.pundir@...aro.org>

>
> Signed-off-by: Kalyan Thota <kalyan_t@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> index 7ea90d2..315b999 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> @@ -151,7 +151,7 @@ static void _dpu_plane_calc_bw(struct drm_plane *plane,
>         u64 plane_bw;
>         u32 hw_latency_lines;
>         u64 scale_factor;
> -       int vbp, vpw;
> +       int vbp, vpw, vfp;
>
>         pstate = to_dpu_plane_state(plane->state);
>         mode = &plane->state->crtc->mode;
> @@ -164,6 +164,7 @@ static void _dpu_plane_calc_bw(struct drm_plane *plane,
>         fps = drm_mode_vrefresh(mode);
>         vbp = mode->vtotal - mode->vsync_end;
>         vpw = mode->vsync_end - mode->vsync_start;
> +       vfp = mode->vsync_start - mode->vdisplay;
>         hw_latency_lines =  dpu_kms->catalog->perf.min_prefill_lines;
>         scale_factor = src_height > dst_height ?
>                 mult_frac(src_height, 1, dst_height) : 1;
> @@ -176,7 +177,13 @@ static void _dpu_plane_calc_bw(struct drm_plane *plane,
>                 src_width * hw_latency_lines * fps * fmt->bpp *
>                 scale_factor * mode->vtotal;
>
> -       do_div(plane_prefill_bw, (vbp+vpw));
> +       if ((vbp+vpw) > hw_latency_lines)
> +               do_div(plane_prefill_bw, (vbp+vpw));
> +       else if ((vbp+vpw+vfp) < hw_latency_lines)
> +               do_div(plane_prefill_bw, (vbp+vpw+vfp));
> +       else
> +               do_div(plane_prefill_bw, hw_latency_lines);
> +
>
>         pstate->plane_fetch_bw = max(plane_bw, plane_prefill_bw);
>  }
> --
> 2.7.4
>