linux-kernel - Re: [RESEND 4/5] drm/mxsfb: Add PM

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Date:   Mon, 17 Sep 2018 21:37:48 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Leonard Crestez <leonard.crestez@....com>
Cc:     Marek Vasut <marex@...x.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Dong Aisheng <aisheng.dong@....com>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        Robert Chiras <robert.chiras@....com>,
        dri-devel@...ts.freedesktop.org, kernel@...gutronix.de,
        Fabio Estevam <fabio.estevam@....com>,
        Marco Franchi <marco.franchi@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-imx@....com
Subject: Re: [RESEND 4/5] drm/mxsfb: Add PM_SLEEP support

Hi Leonard.

On Mon, Aug 27, 2018 at 02:10:40PM +0300, Leonard Crestez wrote:
> Since power to the lcdif block can be lost on suspend implement
> PM_SLEEP_OPS using drm_mode_config_helper_suspend/resume to save/restore
> the current mode.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@....com>
> Reviewed-by: Stefan Agner <stefan@...er.ch>
> ---
>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> index 68d79f5dc0d3..d797dfd40d98 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> @@ -416,17 +416,38 @@ static int mxsfb_remove(struct platform_device *pdev)
>  	drm_dev_unref(drm);
>  
>  	return 0;
>  }
>  
> +#ifdef CONFIG_PM_SLEEP
> +static int mxsfb_suspend(struct device *dev)
> +{
> +       struct drm_device *drm = dev_get_drvdata(dev);
> +
> +       return drm_mode_config_helper_suspend(drm);
> +}
> +
> +static int mxsfb_resume(struct device *dev)
> +{
> +       struct drm_device *drm = dev_get_drvdata(dev);
> +
> +       return drm_mode_config_helper_resume(drm);
> +}
> +#endif

Other suspend/resume users skip the #ifdef and declare
the functions __maybe_unused
See for example arm/hdlcd_drv.c.

The resulting code is a bit simpler to read and you
have the added benefit that the suspend/resume functions
are always compiled so bit-rotting is less likely.

	Sam