[PATCH v5 3/6] drm/mediatek: Detect CMDQ execution timeout

[Chun-Kuang Hu]

Hi, Fei:

Fei Shao <fshao at chromium.org> 於 2021年10月28日 週四 上午11:19寫道：
>
> Hi Chun-Kuang,
>
> On Thu, Oct 28, 2021 at 7:47 AM Chun-Kuang Hu <chunkuang.hu at kernel.org> wrote:
> >
> > Hi, Fei:
> >
> > Fei Shao <fshao at chromium.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 at mediatek.com> wrote:
> > > >
> > > > From: Chun-Kuang Hu <chunkuang.hu at kernel.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 at kernel.org>
> > > > Signed-off-by: jason-jh.lin <jason-jh.lin at mediatek.com>
> > > > Reviewed-by: Chun-Kuang Hu <chunkuang.hu at kernel.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.

I find one thing so that I would like this version. If we do not check
mtk_crtc->cmdq_vblank_cnt > 0, mtk_crtc->cmdq_vblank_cnt would
decrease to minus. And one day it would round to positive. So I would
pick this version instead of v6.

Regards,
Chun-Kuang.

>
>
> >
> > >
> > > > +               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
> > > >