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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Date:   Tue, 1 Nov 2022 11:16:37 +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: Thursday, October 27, 2022 11:11 PM
> To: Vinod Polimera <vpolimer@....qualcomm.com>; 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 27/10/2022 16:34, Vinod Polimera wrote:
> >> -----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.
> 
> Yes. But there is no interlock between commit->hw_done and vblank IRQ
> processing, isn't it? This call happens when DPU processes the vblank
> IRQ, so nobody stops other core from swapping the encode state on
> another core.

https://patchwork.kernel.org/project/linux-arm-msm/patch/1667300361-14572-1-git-send-email-quic_kalyant@quicinc.com/
(drm/msm/disp/dpu1: register crtc color management to first crtc in the list)

The above patch pins 1 crtc to 1 encoder, so it will be safe to assume that crtc wont change.

> >>>
> >>>        DPU_ATRACE_END("encoder_vblank_callback");
> >>>    }
> >> --
> >> With best wishes
> >> Dmitry
> >
> > Thanks,
> > Vinod P.
> 
> --
> With best wishes
> Dmitry

Thanks,
Vinod P.