linux-kernel - Re: [v1 2/2] drm/panel: ili9882t: Avoid blurred screen from fast sleep

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Message-ID: <CAD=FV=W3ef3vWrWRDPKgeUjcapEticj4=EWdC-bOb=ph0DShsA@mail.gmail.com>
Date:   Mon, 9 Oct 2023 13:44:34 -0700
From:   Doug Anderson <dianders@...gle.com>
To:     Cong Yang <yangcong5@...qin.corp-partner.google.com>
Cc:     sam@...nborg.org, neil.armstrong@...aro.org, daniel@...ll.ch,
        hsinyi@...gle.com, linus.walleij@...aro.org, swboyd@...omium.org,
        airlied@...il.com, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [v1 2/2] drm/panel: ili9882t: Avoid blurred screen from fast sleep

Hi,

On Fri, Oct 6, 2023 at 11:07 PM Cong Yang
<yangcong5@...qin.corp-partner.google.com> wrote:
>
> At present, we have found that there may be a problem of blurred
> screen during fast sleep/resume. The direct cause of the blurred
> screen is that the IC does not receive 0x28/0x10. Because of the
> particularity of the IC, before the panel enters sleep hid must
> stop scanning, i2c_hid_core_suspend before ili9882t_disable.
> This doesn't look very spec-compliant.

Presumably you could be more spec compliant if we used
"panel_follower" in this case? Would that be a better solution?


> So in order to solve this
> problem, the IC can handle it through the exception mechanism when
> it cannot receive 0X28/0X10 command. Handling exceptions requires a reset
> 50ms delay. Refer to vendor detailed analysis [1].
>
> Ilitek vendor also suggested switching the page before entering sleep to
> avoid panel IC not receiving 0x28/0x10 command.
>
> Note: 0x28 is display off, 0x10 is sleep in.
>
> [1]: https://github.com/ILITEK-LoganLin/Document/tree/main/ILITEK_Power_Sequence
>
> Signed-off-by: Cong Yang <yangcong5@...qin.corp-partner.google.com>
> ---
>  drivers/gpu/drm/panel/panel-ilitek-ili9882t.c | 21 ++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/panel/panel-ilitek-ili9882t.c b/drivers/gpu/drm/panel/panel-ilitek-ili9882t.c
> index bbfcffe65623..0a1dd987b204 100644
> --- a/drivers/gpu/drm/panel/panel-ilitek-ili9882t.c
> +++ b/drivers/gpu/drm/panel/panel-ilitek-ili9882t.c
> @@ -423,6 +423,23 @@ static inline struct ili9882t *to_ili9882t(struct drm_panel *panel)
>         return container_of(panel, struct ili9882t, base);
>  }
>
> +static int ili9882t_switch_page(struct mipi_dsi_device *dsi, u8 page)
> +{
> +       u8 switch_cmd[] = {0x98, 0x82, 0x00};

Can't you just replace the last 0x00 above with "page" and get rid of
the manual assignment below?


> +       int ret;
> +
> +       switch_cmd[2] = page;
> +
> +       ret = mipi_dsi_dcs_write(dsi, ILI9882T_DCS_SWITCH_PAGE, switch_cmd, 3);

Instead of hardcoding 3, should use ARRAY_SIZE().


> +       if (ret) {
> +               dev_err(&dsi->dev,
> +                       "error switching panel controller page (%d)\n", ret);
> +               return ret;
> +       }
> +
> +       return 0;
> +}

optional: It feels like it would be nice to somehow use the
"_INIT_SWITCH_PAGE_CMD" macro I suggested in patch #1 instead of
having to hardcode 0x98, 0x82 again. In patch #1 I already suggested
breaking out the function to send a sequence of commands. If you had
that function take a pointer instead of hardcoding it to look at
->init_cmds then you could probably use the same function that you do
at init time?


>  static int ili9882t_enter_sleep_mode(struct ili9882t *ili)
>  {
>         struct mipi_dsi_device *dsi = ili->dsi;
> @@ -444,8 +461,10 @@ static int ili9882t_enter_sleep_mode(struct ili9882t *ili)
>  static int ili9882t_disable(struct drm_panel *panel)
>  {
>         struct ili9882t *ili = to_ili9882t(panel);
> +       struct mipi_dsi_device *dsi = ili->dsi;
>         int ret;
>
> +       ili9882t_switch_page(dsi, 0x00);
>         ret = ili9882t_enter_sleep_mode(ili);
>         if (ret < 0) {
>                 dev_err(panel->dev, "failed to set panel off: %d\n", ret);
> @@ -507,7 +526,7 @@ static int ili9882t_prepare(struct drm_panel *panel)
>         gpiod_set_value(ili->enable_gpio, 1);
>         usleep_range(1000, 2000);
>         gpiod_set_value(ili->enable_gpio, 0);
> -       usleep_range(1000, 2000);
> +       usleep_range(40000, 50000);

nit: use 40000, 41000 instead of 40000, 50000. Linux almost always
uses the longer delay, so that'll save ~9 ms. The only reason for the
range is to optimize kernel wakeups which is really not a concern
here.