linux-kernel - Re: [PATCH] drm/panel: simple: Support reset GPIOs

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Message-ID: <20191214102354.GB2967@ravnborg.org>
Date:   Sat, 14 Dec 2019 11:23:54 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH] drm/panel: simple: Support reset GPIOs

Hi Miquel.

On Fri, Dec 13, 2019 at 07:13:25PM +0100, Miquel Raynal wrote:
> The panel common bindings provide a gpios-reset property which is
> active low by default. Let's support it in the simple driver.
> 
> De-asserting the reset pin implies a physical high, which in turns is
> a logic low.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>

Code looks fine - but I fail to see why simple panels would require a
reset pin.

Do you have any simple panels that requires this, or did you add it
because you saw it in the panel-common.yaml file?

	Sam


> ---
>  drivers/gpu/drm/panel/panel-simple.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 5d487686d25c..15dd495c347d 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -110,6 +110,7 @@ struct panel_simple {
>  	struct i2c_adapter *ddc;
>  
>  	struct gpio_desc *enable_gpio;
> +	struct gpio_desc *reset_gpio;
>  
>  	struct drm_display_mode override_mode;
>  };
> @@ -433,12 +434,21 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>  	if (IS_ERR(panel->supply))
>  		return PTR_ERR(panel->supply);
>  
> +	panel->reset_gpio = devm_gpiod_get_optional(dev, "reset",
> +						    GPIOD_OUT_LOW);
> +	if (IS_ERR(panel->reset_gpio)) {
> +		err = PTR_ERR(panel->reset_gpio);
> +		if (err != -EPROBE_DEFER)
> +			dev_err(dev, "failed to request reset pin: %d\n", err);
> +		return err;
> +	}
> +
>  	panel->enable_gpio = devm_gpiod_get_optional(dev, "enable",
>  						     GPIOD_OUT_LOW);
>  	if (IS_ERR(panel->enable_gpio)) {
>  		err = PTR_ERR(panel->enable_gpio);
>  		if (err != -EPROBE_DEFER)
> -			dev_err(dev, "failed to request GPIO: %d\n", err);
> +			dev_err(dev, "failed to request enable pin: %d\n", err);
>  		return err;
>  	}
>  
> -- 
> 2.20.1