linux-kernel - Re: [PATCH v5 3/6] drm/mediatek: Detect CMDQ execution timeout

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Message-ID: <CAC=S1njhuzPi6gOmGfqhtKMtDTsGPzZ7P=PoVbAviHt1o00U6w@mail.gmail.com>
Date:   Thu, 28 Oct 2021 11:19:04 +0800
From:   Fei Shao <fshao@...omium.org>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>
Cc:     "jason-jh.lin" <jason-jh.lin@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Yongqiang Niu <yongqiang.niu@...iatek.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Nancy Lin <nancy.lin@...iatek.com>, singo.chang@...iatek.com
Subject: Re: [PATCH v5 3/6] drm/mediatek: Detect CMDQ execution timeout

Hi Chun-Kuang,

On Thu, Oct 28, 2021 at 7:47 AM Chun-Kuang Hu <chunkuang.hu@...nel.org> wrote:
>
> Hi, Fei:
>
> Fei Shao <fshao@...omium.org> 於 2021年10月27日 週三 下午5:32寫道：
> >
> > Hi Jason,
> >
> > On Wed, Oct 27, 2021 at 10:19 AM jason-jh.lin <jason-jh.lin@...iatek.com> wrote:
> > >
> > > From: Chun-Kuang Hu <chunkuang.hu@...nel.org>
> > >
> > > CMDQ is used to update display register in vblank period, so
> > > it should be execute in next 2 vblank. One vblank interrupt
> > > before send message (occasionally) and one vblank interrupt
> > > after cmdq done. If it fail to execute in next 3 vblank,
> > > tiemout happen.
> > >
> > > Signed-off-by: Chun-Kuang Hu <chunkuang.hu@...nel.org>
> > > Signed-off-by: jason-jh.lin <jason-jh.lin@...iatek.com>
> > > Reviewed-by: Chun-Kuang Hu <chunkuang.hu@...nel.org>
> > > ---
> > >  drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 20 ++++++++++++++++++--
> > >  1 file changed, 18 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> > > index e23e3224ac67..dad1f85ee315 100644
> > > --- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> > > +++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> > > @@ -54,6 +54,7 @@ struct mtk_drm_crtc {
> > >  #if IS_REACHABLE(CONFIG_MTK_CMDQ)
> > >         struct cmdq_client              cmdq_client;
> > >         u32                             cmdq_event;
> > > +       u32                             cmdq_vblank_cnt;
> > >  #endif
> > >
> > >         struct device                   *mmsys_dev;
> > > @@ -227,7 +228,10 @@ struct mtk_ddp_comp *mtk_drm_ddp_comp_for_plane(struct drm_crtc *crtc,
> > >  static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
> > >  {
> > >         struct cmdq_cb_data *data = mssg;
> > > +       struct cmdq_client *cmdq_cl = container_of(cl, struct cmdq_client, client);
> > > +       struct mtk_drm_crtc *mtk_crtc = container_of(cmdq_cl, struct mtk_drm_crtc, cmdq_client);
> > >
> > > +       mtk_crtc->cmdq_vblank_cnt = 0;
> > >         cmdq_pkt_destroy(data->pkt);
> > >  }
> > >  #endif
> > > @@ -483,6 +487,15 @@ static void mtk_drm_crtc_update_config(struct mtk_drm_crtc *mtk_crtc,
> > >                                            cmdq_handle->pa_base,
> > >                                            cmdq_handle->cmd_buf_size,
> > >                                            DMA_TO_DEVICE);
> > > +               /*
> > > +                * CMDQ command should execute in next 3 vblank.
> > > +                * One vblank interrupt before send message (occasionally)
> > > +                * and one vblank interrupt after cmdq done,
> > > +                * so it's timeout after 3 vblank interrupt.
> > > +                * If it fail to execute in next 3 vblank, timeout happen.
> > > +                */
> > > +               mtk_crtc->cmdq_vblank_cnt = 3;
> > > +
> > >                 mbox_send_message(mtk_crtc->cmdq_client.chan, cmdq_handle);
> > >                 mbox_client_txdone(mtk_crtc->cmdq_client.chan, 0);
> > >         }
> > > @@ -499,11 +512,14 @@ static void mtk_crtc_ddp_irq(void *data)
> > >
> > >  #if IS_REACHABLE(CONFIG_MTK_CMDQ)
> > >         if (!priv->data->shadow_register && !mtk_crtc->cmdq_client.chan)
> > > +               mtk_crtc_ddp_config(crtc, NULL);
> > > +       else if (mtk_crtc->cmdq_vblank_cnt > 0 && --mtk_crtc->cmdq_vblank_cnt == 0)
> > I think atomic_dec_and_test() does what you want to do here.
>
> I think this operation is not necessary to be atomic operation, and
> this statement could be reduced to
>
> else if (--mtk_crtc->cmdq_vblank_cnt == 0)

I was thinking about using existing helpers to wrap up the counter
operations, but I agree that it's not necessary.
Just dropping the redundant check would be good enough.


>
> >
> > > +               DRM_ERROR("mtk_crtc %d CMDQ execute command timeout!\n",
> > > +                         drm_crtc_index(&mtk_crtc->base));
> > >  #else
> > >         if (!priv->data->shadow_register)
> > > -#endif
> > >                 mtk_crtc_ddp_config(crtc, NULL);
> > > -
> > > +#endif
> > >         mtk_drm_finish_page_flip(mtk_crtc);
> > >  }
> > >
> > > --
> > > 2.18.0
> > >