linux-kernel - Re: [PATCH] drm/panel: ilitek-ili9881c: Avoid unbalance prepare/unprepare

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Message-ID: <CAOf5uw=DffhS=WAh-OFXOCO+4kd5ey=2Eqf0Zhyrgd_d5D8meA@mail.gmail.com>
Date:   Thu, 9 Dec 2021 11:17:17 +0100
From:   Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>
Cc:     Daniel Vetter <daniel@...ll.ch>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: ilitek-ili9881c: Avoid unbalance prepare/unprepare

Hi all

On Sat, Oct 16, 2021 at 4:58 PM Michael Trimarchi
<michael@...rulasolutions.com> wrote:
>
> All the panel driver check the fact that their prepare/unprepare
> call was already called. It's not an ideal solution but fix
> for now the problem on ili9881c
>
> [ 9862.283296] ------------[ cut here ]------------
> [ 9862.288490] unbalanced disables for vcc3v3_lcd
> [ 9862.293555] WARNING: CPU: 0 PID: 1 at drivers/regulator/core.c:2851
> _regulator_disable+0xd4/0x190
>
> from:
>
> [ 9862.038619]  drm_panel_unprepare+0x2c/0x4c
> [ 9862.043212]  panel_bridge_post_disable+0x18/0x24
> [ 9862.048390]  dw_mipi_dsi_bridge_post_disable+0x3c/0xf0
> [ 9862.054153]  drm_atomic_bridge_chain_post_disable+0x8c/0xd0
>
> and:
>
> [ 9862.183103]  drm_panel_unprepare+0x2c/0x4c
> [ 9862.187695]  panel_bridge_post_disable+0x18/0x24
> [ 9862.192872]  drm_atomic_bridge_chain_post_disable+0x8c/0xd0
> [ 9862.199117]  disable_outputs+0x120/0x31c
>
> Signed-off-by: Michael Trimarchi <michael@...rulasolutions.com>
> ---
>  drivers/gpu/drm/panel/panel-ilitek-ili9881c.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
> index 103a16018975..f75eecb0e65c 100644
> --- a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
> +++ b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
> @@ -52,6 +52,8 @@ struct ili9881c {
>
>         struct regulator        *power;
>         struct gpio_desc        *reset;
> +
> +       bool                    prepared;
>  };
>

I found that this can be a general problem. Should not mandatory to
track panel status

DRM_PANEL_PREPARED
DRM_PANEL_ENABLED

Michael
>  #define ILI9881C_SWITCH_PAGE_INSTR(_page)      \
> @@ -707,6 +709,10 @@ static int ili9881c_prepare(struct drm_panel *panel)
>         unsigned int i;
>         int ret;
>
> +       /* Preparing when already prepared is a no-op */
> +       if (ctx->prepared)
> +               return 0;
> +
>         /* Power the panel */
>         ret = regulator_enable(ctx->power);
>         if (ret)
> @@ -745,6 +751,8 @@ static int ili9881c_prepare(struct drm_panel *panel)
>         if (ret)
>                 return ret;
>
> +       ctx->prepared = true;
> +
>         return 0;
>  }
>
> @@ -770,10 +778,16 @@ static int ili9881c_unprepare(struct drm_panel *panel)
>  {
>         struct ili9881c *ctx = panel_to_ili9881c(panel);
>
> +       /* Unpreparing when already unprepared is a no-op */
> +       if (!ctx->prepared)
> +               return 0;
> +
>         mipi_dsi_dcs_enter_sleep_mode(ctx->dsi);
>         regulator_disable(ctx->power);
>         gpiod_set_value(ctx->reset, 1);
>
> +       ctx->prepared = false;
> +
>         return 0;
>  }
>
> --
> 2.25.1
>


-- 
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael@...rulasolutions.com
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