linux-kernel - Re: [PATCH 2/3] drm/sitronix/st7571-i2c: Make the reset GPIO to be optional

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Message-ID: <a5cb70b2-f724-4d5e-910c-0b92dd759ebf@suse.de>
Date: Mon, 14 Jul 2025 10:55:57 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Javier Martinez Canillas <javierm@...hat.com>,
 linux-kernel@...r.kernel.org
Cc: ipedrosa@...hat.com, David Airlie <airlied@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Marcus Folkesson <marcus.folkesson@...il.com>,
 Maxime Ripard <mripard@...nel.org>, Simona Vetter <simona@...ll.ch>,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 2/3] drm/sitronix/st7571-i2c: Make the reset GPIO to be
 optional

Hi

Am 10.07.25 um 12:24 schrieb Javier Martinez Canillas:
> Some Sitronix LCD controllers (such as the ST7567) don't have a reset pin,
> so lets relax this in the driver and make the reset GPIO to be optional.
>
> The devm_gpiod_get_optional() helper is similar to devm_gpiod_get(), but
> returns NULL when there isn't a reset-gpios property defined in a DT node.
>
> The DT binding schema for "sitronix,st7571" that require a reset GPIO will
> enforce the "reset-gpios" to be present, due being a required DT property.
> But in the driver itself the property can be made optional if not defined.
>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
>
>   drivers/gpu/drm/sitronix/st7571-i2c.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/sitronix/st7571-i2c.c b/drivers/gpu/drm/sitronix/st7571-i2c.c
> index eec846892962..73e8db25f895 100644
> --- a/drivers/gpu/drm/sitronix/st7571-i2c.c
> +++ b/drivers/gpu/drm/sitronix/st7571-i2c.c
> @@ -802,15 +802,19 @@ static int st7571_parse_dt(struct st7571_device *st7571)
>   	st7571->nlines = dt.vactive.typ;
>   	st7571->ncols = dt.hactive.typ;
>   
> -	st7571->reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
> +	st7571->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
>   	if (IS_ERR(st7571->reset))
> -		return PTR_ERR(st7571->reset);
> +		return dev_err_probe(dev, PTR_ERR(st7571->reset),
> +				     "Failed to get reset gpio\n");

There's struct st7571_panel_data. It could store a flag signalling the 
expected behavior.

With more effort the panel_data could store a dedicated parse_dt pointer 
for each panel type. ASAICT the st7567 features a subset of the other 
type. So there might not be much code duplication.

Best regards
Thomas

>   
>   	return 0;
>   }
>   
>   static void st7571_reset(struct st7571_device *st7571)
>   {
> +	if (!st7571->reset)
> +		return;
> +
>   	gpiod_set_value_cansleep(st7571->reset, 1);
>   	fsleep(20);
>   	gpiod_set_value_cansleep(st7571->reset, 0);

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)