linux-kernel - RE: [PATCH v8 01/15] drm/msm/disp/dpu: clear dpu_assign_crtc and get crtc from connector state instead of dpu

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Message-ID: <BN0PR02MB8173F084DD0DDAD2E312CA6DE4339@BN0PR02MB8173.namprd02.prod.outlook.com>
Date:   Thu, 27 Oct 2022 13:34:44 +0000
From:   Vinod Polimera <vpolimer@....qualcomm.com>
To:     "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "Vinod Polimera (QUIC)" <quic_vpolimer@...cinc.com>,
        "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>
CC:     "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>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
Subject: RE: [PATCH v8 01/15] drm/msm/disp/dpu: clear dpu_assign_crtc and get
 crtc from connector state instead of dpu_enc

> -----Original Message-----
> From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Sent: Monday, October 24, 2022 8:52 PM
> To: Vinod Polimera (QUIC) <quic_vpolimer@...cinc.com>; dri-
> devel@...ts.freedesktop.org; linux-arm-msm@...r.kernel.org;
> freedreno@...ts.freedesktop.org; devicetree@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org; robdclark@...il.com;
> dianders@...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>; Aravind Venkateswaran (QUIC)
> <quic_aravindh@...cinc.com>; Abhinav Kumar (QUIC)
> <quic_abhinavk@...cinc.com>; Sankeerth Billakanti (QUIC)
> <quic_sbillaka@...cinc.com>
> Subject: Re: [PATCH v8 01/15] drm/msm/disp/dpu: clear dpu_assign_crtc and
> get crtc from connector state instead of dpu_enc
> 
> WARNING: This email originated from outside of Qualcomm. Please be wary
> of any links or attachments, and do not enable macros.
> 
> On 12/10/2022 15:02, Vinod Polimera wrote:
> > Update crtc retrieval from dpu_enc to dpu_enc connector state,
> > since new links get set as part of the dpu enc virt mode set.
> > The dpu_enc->crtc cache is no more needed, hence cleaning it as
> > part of this change.
> >
> > Signed-off-by: Vinod Polimera <quic_vpolimer@...cinc.com>
> > ---
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c    |  4 ---
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 42 +++++++++---------
> -----------
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h |  8 ------
> >   3 files changed, 13 insertions(+), 41 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > index 13ce321..8ec9a13 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > @@ -1029,7 +1029,6 @@ static void dpu_crtc_disable(struct drm_crtc *crtc,
> >                */
> >               if (dpu_encoder_get_intf_mode(encoder) == INTF_MODE_VIDEO)
> >                       release_bandwidth = true;
> > -             dpu_encoder_assign_crtc(encoder, NULL);
> >       }
> >
> >       /* wait for frame_event_done completion */
> > @@ -1099,9 +1098,6 @@ static void dpu_crtc_enable(struct drm_crtc *crtc,
> >       trace_dpu_crtc_enable(DRMID(crtc), true, dpu_crtc);
> >       dpu_crtc->enabled = true;
> >
> > -     drm_for_each_encoder_mask(encoder, crtc->dev, crtc->state-
> >encoder_mask)
> > -             dpu_encoder_assign_crtc(encoder, crtc);
> > -
> >       /* Enable/restore vblank irq handling */
> >       drm_crtc_vblank_on(crtc);
> >   }
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > index 9c6817b..d05b353 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > @@ -132,11 +132,6 @@ enum dpu_enc_rc_states {
> >    * @intfs_swapped:  Whether or not the phys_enc interfaces have been
> swapped
> >    *                  for partial update right-only cases, such as pingpong
> >    *                  split where virtual pingpong does not generate IRQs
> > - * @crtc:            Pointer to the currently assigned crtc. Normally you
> > - *                   would use crtc->state->encoder_mask to determine the
> > - *                   link between encoder/crtc. However in this case we need
> > - *                   to track crtc in the disable() hook which is called
> > - *                   _after_ encoder_mask is cleared.
> >    * @connector:              If a mode is set, cached pointer to the active
> connector
> >    * @crtc_kickoff_cb:                Callback into CRTC that will flush & start
> >    *                          all CTL paths
> > @@ -181,7 +176,6 @@ struct dpu_encoder_virt {
> >
> >       bool intfs_swapped;
> >
> > -     struct drm_crtc *crtc;
> >       struct drm_connector *connector;
> >
> >       struct dentry *debugfs_root;
> > @@ -1288,7 +1282,7 @@ static void dpu_encoder_vblank_callback(struct
> drm_encoder *drm_enc,
> >               struct dpu_encoder_phys *phy_enc)
> >   {
> >       struct dpu_encoder_virt *dpu_enc = NULL;
> > -     unsigned long lock_flags;
> > +     struct drm_crtc *crtc;
> >
> >       if (!drm_enc || !phy_enc)
> >               return;
> > @@ -1296,12 +1290,13 @@ static void dpu_encoder_vblank_callback(struct
> drm_encoder *drm_enc,
> >       DPU_ATRACE_BEGIN("encoder_vblank_callback");
> >       dpu_enc = to_dpu_encoder_virt(drm_enc);
> >
> > -     atomic_inc(&phy_enc->vsync_cnt);
> > +     if (!dpu_enc->connector || !dpu_enc->connector->state ||
> > +         !dpu_enc->connector->state->crtc)
> > +             return;
> >
> > -     spin_lock_irqsave(&dpu_enc->enc_spinlock, lock_flags);
> > -     if (dpu_enc->crtc)
> > -             dpu_crtc_vblank_callback(dpu_enc->crtc);
> > -     spin_unlock_irqrestore(&dpu_enc->enc_spinlock, lock_flags);
> > +     atomic_inc(&phy_enc->vsync_cnt);
> > +     crtc = dpu_enc->connector->state->crtc;
> > +     dpu_crtc_vblank_callback(crtc);
> 
> So, what if the user commits the mode setting change on another CPU,
> while we are handling the vblank callback here? Can this happen?
> 
If user issues a commit on another CPU, it will wait in the drm_atomic_helper_swap_state
as drm_atomic_helper_commit_hw_done which does the complete_all(&commit->hw_done) 
for the current commit didn't finish yet.
> >
> >       DPU_ATRACE_END("encoder_vblank_callback");
> >   }
> --
> With best wishes
> Dmitry

Thanks,
Vinod P.