linux-kernel - Re: [PATCH 2/4] drm: panel: sofef00: remove reset GPIO handling

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Message-ID: <YK0ZbTeH7eRP+p98@builder.lan>
Date:   Tue, 25 May 2021 10:36:13 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Caleb Connolly <caleb@...nolly.tech>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] drm: panel: sofef00: remove reset GPIO handling

On Sat 01 May 20:42 CDT 2021, Caleb Connolly wrote:

> Resetting the panel on fajita causes it to never come back, we aren't
> quite sure why this is so for now lets remove reset handling as it is
> effectively broken. It is also not needed on enchilada.
> 
> Signed-off-by: Caleb Connolly <caleb@...nolly.tech>
> ---
>  drivers/gpu/drm/panel/panel-samsung-sofef00.c | 26 +++----------------
>  1 file changed, 4 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-samsung-sofef00.c b/drivers/gpu/drm/panel/panel-samsung-sofef00.c
> index 8cb1853574bb..cfc8b2a19742 100644
> --- a/drivers/gpu/drm/panel/panel-samsung-sofef00.c
> +++ b/drivers/gpu/drm/panel/panel-samsung-sofef00.c
> @@ -23,7 +23,6 @@ struct sofef00_panel {
>  	struct drm_panel panel;
>  	struct mipi_dsi_device *dsi;
>  	struct regulator *supply;
> -	struct gpio_desc *reset_gpio;
>  	const struct drm_display_mode *mode;
>  	bool prepared;
>  };
> @@ -42,16 +41,6 @@ struct sofef00_panel *to_sofef00_panel(struct drm_panel *panel)
>  			return ret;					\
>  	} while (0)
>  
> -static void sofef00_panel_reset(struct sofef00_panel *ctx)
> -{
> -	gpiod_set_value_cansleep(ctx->reset_gpio, 0);
> -	usleep_range(5000, 6000);
> -	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
> -	usleep_range(2000, 3000);
> -	gpiod_set_value_cansleep(ctx->reset_gpio, 0);
> -	usleep_range(12000, 13000);
> -}
> -
>  static int sofef00_panel_on(struct sofef00_panel *ctx)
>  {
>  	struct mipi_dsi_device *dsi = ctx->dsi;
> @@ -132,12 +121,9 @@ static int sofef00_panel_prepare(struct drm_panel *panel)
>  		return ret;
>  	}
>  
> -	sofef00_panel_reset(ctx);
> -
>  	ret = sofef00_panel_on(ctx);
>  	if (ret < 0) {
>  		dev_err(dev, "Failed to initialize panel: %d\n", ret);
> -		gpiod_set_value_cansleep(ctx->reset_gpio, 1);
>  		return ret;
>  	}
>  
> @@ -155,8 +141,11 @@ static int sofef00_panel_unprepare(struct drm_panel *panel)
>  		return 0;
>  
>  	ret = sofef00_panel_off(ctx);
> -	if (ret < 0)
> +
> +	if (ret < 0) {
>  		dev_err(dev, "Failed to un-initialize panel: %d\n", ret);
> +		return ret;

This early return seems unrelated to what's described in the commit
message.

Also as a general comment, what do you expect the software should do if
you return an error in the unprepare path? Can we if this happens just
continue to display stuff on the display?

> +	}
>  
>  	regulator_disable(ctx->supply);
>  
> @@ -276,13 +265,6 @@ static int sofef00_panel_probe(struct mipi_dsi_device *dsi)
>  		return ret;
>  	}
>  
> -	ctx->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);

If I understand your description in the cover letter this works for one
of the devices using the panel, but not the other.

So how about using devm_gpiod_get_optional() instead. That will give you
NULL back if the property isn't defined and make all the gpiod
operations nops.

Regards,
Bjorn

> -	if (IS_ERR(ctx->reset_gpio)) {
> -		ret = PTR_ERR(ctx->reset_gpio);
> -		dev_warn(dev, "Failed to get reset-gpios: %d\n", ret);
> -		return ret;
> -	}
> -
>  	ctx->dsi = dsi;
>  	mipi_dsi_set_drvdata(dsi, ctx);
>  
> -- 
> 2.30.2
> 
>