linux-kernel - RE: [PATCH v1 1/3] drm/msm/dpu: set dirty

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Date:   Mon, 3 Apr 2023 14:53:29 +0000
From:   Vinod Polimera <vpolimer@....qualcomm.com>
To:     "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "Vinod Polimera (QUIC)" <quic_vpolimer@...cinc.com>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>,
        "Kalyan Thota (QUIC)" <quic_kalyant@...cinc.com>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        "Vishnuvardhan Prodduturi (QUIC)" <quic_vproddut@...cinc.com>,
        "Bjorn Andersson (QUIC)" <quic_bjorande@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
Subject: RE: [PATCH v1 1/3] drm/msm/dpu: set dirty_fb flag while in self
 refresh mode

> On Fri, 31 Mar 2023 at 16:59, Vinod Polimera <quic_vpolimer@...cinc.com>
> wrote:
> >
> > While in virtual terminal mode with PSR enabled, there will be
> > no atomic commits triggered without dirty_fb being set. This
> > will create a notion of no screen update. Allow atomic commit
> > when dirty_fb ioctl is issued, so that it can trigger a PSR exit
> > and shows update on the screen.
> 
> Will this impact non-VT workloads? If I remember correctly, we added
> dirty_fb handling to prevent the framework from limiting the page
> flips to vblank events (in DSI video mode).
> 
From the use case referred in the commit text ( 9e4dde28e  drm/msm: Avoid dirtyfb stalls on video mode displays (v2)).
There can be an impact on the workload. I can think of two solutions:
1) Add modparam to configure PSR wait time (SELF_REFRESH_AVG_SEED_MS 200) and application can set it to "-1" if they are operating on dirty_fb
2) In msm drivers, disable psr if dirty_fb_ioctl is requested from the framework and re-enable it during regular commit.
    This will involve copying dirtyflags from drm fb ->msm_fb->dpu_plane and add atomic_check failure if ( dirty_flags &&  self_refresh_active).

Please let me know your thoughts on the above two.

Thanks,
Vinod.

> >
> > Reported-by: Bjorn Andersson <andersson@...nel.org>
> > Link:
> https://lore.kernel.org/all/20230326162723.3lo6pnsfdwzsvbhj@ripper/
> > Signed-off-by: Vinod Polimera <quic_vpolimer@...cinc.com>
> > ---
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > index ab636da..96f645e 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > @@ -1158,6 +1158,9 @@ static bool dpu_crtc_needs_dirtyfb(struct
> drm_crtc_state *cstate)
> >         struct drm_crtc *crtc = cstate->crtc;
> >         struct drm_encoder *encoder;
> >
> > +       if (cstate->self_refresh_active)
> > +               return true;
> > +
> >         drm_for_each_encoder_mask (encoder, crtc->dev, cstate-
> >encoder_mask) {
> >                 if (dpu_encoder_get_intf_mode(encoder) == INTF_MODE_CMD) {
> >                         return true;
> > --
> > 2.7.4
> >
> 
> 
> --
> With best wishes
> Dmitry