linux-kernel - Re: [RFT PATCH 15/15] drm/renesas/shmobile: Call drm_helper_force_disable

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Date:   Mon, 4 Sep 2023 09:27:48 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     dri-devel@...ts.freedesktop.org,
        Maxime Ripard <mripard@...nel.org>, airlied@...il.com,
        biju.das.jz@...renesas.com, daniel@...ll.ch,
        kieran.bingham+renesas@...asonboard.com,
        laurent.pinchart@...asonboard.com, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, paul@...pouillou.net,
        tzimmermann@...e.de
Subject: Re: [RFT PATCH 15/15] drm/renesas/shmobile: Call drm_helper_force_disable_all()
 at shutdown/remove time

Hi Douglas,

On Sat, Sep 2, 2023 at 1:42 AM Douglas Anderson <dianders@...omium.org> wrote:
> Based on grepping through the source code, this driver appears to be
> missing a call to drm_atomic_helper_shutdown(), or in this case the
> non-atomic equivalent drm_helper_force_disable_all(), at system
> shutdown time and at driver remove time. This is important because
> drm_helper_force_disable_all() will cause panels to get disabled
> cleanly which may be important for their power sequencing. Future
> changes will remove any custom powering off in individual panel
> drivers so the DRM drivers need to start getting this right.
>
> The fact that we should call drm_atomic_helper_shutdown(), or in this
> case the non-atomic equivalent drm_helper_force_disable_all(), in the
> case of OS shutdown/restart comes straight out of the kernel doc
> "driver instance overview" in drm_drv.c.
>
> Suggested-by: Maxime Ripard <mripard@...nel.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Thanks for your patch!

> --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
> +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
> @@ -179,12 +180,20 @@ static int shmob_drm_remove(struct platform_device *pdev)
>
>         drm_dev_unregister(ddev);
>         drm_kms_helper_poll_fini(ddev);
> +       drm_helper_force_disable_all(ddev);

After "[PATCH v3 36/41] drm: renesas: shmobile: Atomic conversion part
1"[1], this function will already call drm_atomic_helper_shutdown()...

>         free_irq(sdev->irq, ddev);
>         drm_dev_put(ddev);
>
>         return 0;
>  }
>
> +static void shmob_drm_shutdown(struct platform_device *pdev)
> +{
> +       struct shmob_drm_device *sdev = platform_get_drvdata(pdev);
> +
> +       drm_helper_force_disable_all(sdev->ddev);

... and this should be replaced by a call to drm_atomic_helper_shutdown().

[1] https://lore.kernel.org/dri-devel/fd7a6702490bd431f314d6591551bb39e77e3304.1692178020.git.geert+renesas@glider.be

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds