linux-kernel - Re: [PATCH 69/78] media: rcar-vin: use pm_runtime_resume_and

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Date:   Sat, 24 Apr 2021 11:12:31 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     Linuxarm <linuxarm@...wei.com>, mauro.chehab@...wei.com,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH 69/78] media: rcar-vin: use pm_runtime_resume_and_get()

Hi Mauro,

On Sat, Apr 24, 2021 at 8:46 AM Mauro Carvalho Chehab
<mchehab+huawei@...nel.org> wrote:
> Commit dd8088d5a896 ("PM: runtime: Add pm_runtime_resume_and_get to deal with usage counter")
> added pm_runtime_resume_and_get() in order to automatically handle
> dev->power.usage_count decrement on errors.
>
> Use the new API, in order to cleanup the error check logic.
>
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>

Thanks for your patch!

> --- a/drivers/media/platform/rcar-vin/rcar-csi2.c
> +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
> @@ -408,7 +408,7 @@ static void rcsi2_enter_standby(struct rcar_csi2 *priv)
>
>  static void rcsi2_exit_standby(struct rcar_csi2 *priv)
>  {
> -       pm_runtime_get_sync(priv->dev);
> +       pm_runtime_resume_and_get(priv->dev);

I believe this part is incorrect: on failure[*], the refcount will now
be decremented, and in a subsequent call to rcsi2_enter_standby(), the
refcount will be decremented again due to the call to pm_runtime_put().

[*] On e.g. R-Car SoCs, this can never fail.  This is the reason why
    many R-Car (and SuperH) drivers never check the result of
    pm_runtime_get_sync().  So the refcount "imbalances" were actually
    introduced by the various "clean up" patches to add return value
    checking, which now need another round of fixing...

>         reset_control_deassert(priv->rstc);
>  }

> --- a/drivers/media/platform/rcar-vin/rcar-dma.c
> +++ b/drivers/media/platform/rcar-vin/rcar-dma.c
> @@ -1458,11 +1458,9 @@ int rvin_set_channel_routing(struct rvin_dev *vin, u8 chsel)
>         u32 vnmc;
>         int ret;
>
> -       ret = pm_runtime_get_sync(vin->dev);
> -       if (ret < 0) {
> -               pm_runtime_put_noidle(vin->dev);
> +       ret = pm_runtime_resume_and_get(vin->dev);
> +       if (ret < 0)
>                 return ret;
> -       }

This change (and the change below) is correct, as the logic before/after
is equivalent.

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