linux-kernel - Re: [PATCH] drm/msm/dsi: skip the wait for video mode done if not applicable

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Message-ID: <CAA8EJpp-eK1spEBSJtT0YtRkJtSL6MWPyxN5c4AB-1MJMJXs9A@mail.gmail.com>
Date:   Fri, 15 Sep 2023 22:02:24 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Hai Li <hali@...eaurora.org>,
        dri-devel@...ts.freedesktop.org, quic_jesszhan@...cinc.com,
        quic_parellan@...cinc.com, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dsi: skip the wait for video mode done if not applicable

On Fri, 15 Sept 2023 at 21:30, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>
> dsi_wait4video_done() API wait for the DSI video mode engine to
> become idle so that we can transmit the DCS commands in the
> beginning of BLLP. However, with the current sequence, the MDP
> timing engine is turned on after the panel's pre_enable() callback
> which can send out the DCS commands needed to power up the panel.
>
> During those cases, this API will always timeout and print out the
> error spam leading to long bootup times and log flooding.
>
> Fix this by checking if the DSI video engine was actually busy before
> waiting for it to become idle otherwise this is a redundant wait.
>
> Fixes: a689554ba6ed ("drm/msm: Initial add DSI connector support")
> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 0c4ec0530efc..31495e423c56 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1075,9 +1075,21 @@ static void dsi_wait4video_done(struct msm_dsi_host *msm_host)
>
>  static void dsi_wait4video_eng_busy(struct msm_dsi_host *msm_host)
>  {
> +       u32 data;
> +
> +       data = dsi_read(msm_host, REG_DSI_STATUS0);
> +
>         if (!(msm_host->mode_flags & MIPI_DSI_MODE_VIDEO))
>                 return;

We can probably skip reading REG_DSI_STATUS0 if the host is in CMD mode.
LGTM otherwise.

>
> +       /* if video mode engine is not busy, its because
> +        * either timing engine was not turned on or the
> +        * DSI controller has finished transmitting the video
> +        * data already, so no need to wait in those cases
> +        */
> +       if (!(data & DSI_STATUS0_VIDEO_MODE_ENGINE_BUSY))
> +               return;
> +
>         if (msm_host->power_on && msm_host->enabled) {
>                 dsi_wait4video_done(msm_host);
>                 /* delay 4 ms to skip BLLP */
> --
> 2.40.1
>


-- 
With best wishes
Dmitry