linux-kernel - Re: [PATCH 2/4] drm/panel: feiyang-fy07024di26a30d: make reset gpio optional

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Date:   Mon, 31 Jan 2022 01:03:35 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     Jagan Teki <jagan@...rulasolutions.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Peter Geis <pgwipeout@...il.com>
Cc:     Peter Geis <pgwipeout@...il.com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] drm/panel: feiyang-fy07024di26a30d: make reset gpio optional

Hi Peter,

Am Freitag, 7. Januar 2022, 06:13:33 CET schrieb Peter Geis:
> Some implementations do not use the reset signal, instead tying it to dvdd.
> Make the reset gpio optional to permit this.
> 
> Signed-off-by: Peter Geis <pgwipeout@...il.com>
> ---
>  drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c b/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c
> index 581661b506f8..1c88d752b14e 100644
> --- a/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c
> +++ b/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c
> @@ -65,7 +65,8 @@ static int feiyang_prepare(struct drm_panel *panel)
>  	/* T3 (dvdd rise + avdd start + avdd rise) T3 >= 20ms */
>  	msleep(20);
>  
> -	gpiod_set_value(ctx->reset, 0);
> +	if (ctx->reset)
> +		gpiod_set_value(ctx->reset, 0);

gpio_set_value does 
	VALIDATE_DESC_VOID(desc);

which checks for "desc" (ctx->reset in this case) to be valid and especially
not null and simply returns when this is the case.

So from what I see, we don't need all the added conditionals here and below
and would just need the switch to devm_gpiod_get_optional alone.

Heiko

>  
>  	/*
>  	 * T5 + T6 (avdd rise + video & logic signal rise)
> @@ -73,7 +74,8 @@ static int feiyang_prepare(struct drm_panel *panel)
>  	 */
>  	msleep(20);
>  
> -	gpiod_set_value(ctx->reset, 1);
> +	if (ctx->reset)
> +		gpiod_set_value(ctx->reset, 1);
>  
>  	/* T12 (video & logic signal rise + backlight rise) T12 >= 200ms */
>  	msleep(200);
> @@ -126,7 +128,8 @@ static int feiyang_unprepare(struct drm_panel *panel)
>  	/* T13 (backlight fall + video & logic signal fall) T13 >= 200ms */
>  	msleep(200);
>  
> -	gpiod_set_value(ctx->reset, 0);
> +	if (ctx->reset)
> +		gpiod_set_value(ctx->reset, 0);
>  
>  	regulator_disable(ctx->avdd);
>  
> @@ -211,7 +214,7 @@ static int feiyang_dsi_probe(struct mipi_dsi_device *dsi)
>  		return PTR_ERR(ctx->avdd);
>  	}
>  
> -	ctx->reset = devm_gpiod_get(&dsi->dev, "reset", GPIOD_OUT_LOW);
> +	ctx->reset = devm_gpiod_get_optional(&dsi->dev, "reset", GPIOD_OUT_LOW);
>  	if (IS_ERR(ctx->reset)) {
>  		dev_err(&dsi->dev, "Couldn't get our reset GPIO\n");
>  		return PTR_ERR(ctx->reset);
>