Subject: Re: [PATCH 1/5] drm/panel: Add helper for reading DT rotation

From: Sam Ravnborg <[email-masked]>
Date: Wed, 12 Jun 2019 23:18:07 +0200

Hi Derek.

On Mon, Jun 10, 2019 at 09:03:46PM -0700, Derek Basehore wrote:
> This adds a helper function for reading the rotation (panel
> orientation) from the device tree.
> 
> Signed-off-by: Derek Basehore <[email-masked]>
> ---
>  drivers/gpu/drm/drm_panel.c | 41 +++++++++++++++++++++++++++++++++++++
>  include/drm/drm_panel.h     |  7 +++++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index dbd5b873e8f2..3b689ce4a51a 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -172,6 +172,47 @@ struct drm_panel *of_drm_find_panel(const struct device_node *np)
>  	return ERR_PTR(-EPROBE_DEFER);
>  }
>  EXPORT_SYMBOL(of_drm_find_panel);
> +
> +/**
> + * of_drm_get_panel_orientation - look up the rotation of the panel using a
> + * device tree node
> + * @np: device tree node of the panel
> + * @orientation: orientation enum to be filled in
The comment says "enum" but the type used is an int.
Why not use enum drm_panel_orientation?

> + *
> + * Looks up the rotation of a panel in the device tree. The rotation in the
> + * device tree is counter clockwise.
> + *
> + * Return: 0 when a valid rotation value (0, 90, 180, or 270) is read or the
> + * rotation property doesn't exist. -EERROR otherwise.
> + */
Initially I read -EEROOR as a specific error code.
But I gues the semantic is to say that a negative error code is returned
if something was wrong.
As we do not use the "-EERROR" syntax anywhere else in drm, please
reword like we do in other places.

Also - it is worth to mention that the rotation returned is
DRM_MODE_PANEL_ORIENTATION_UNKNOWN if the property is not specified.
I wonder if this is correct, as no property could also been
interpretated as DRM_MODE_PANEL_ORIENTATION_NORMAL.
And in most cases the roation property is optional, so one could
assume that no property equals 0 degree.

	Sam

> +int of_drm_get_panel_orientation(const struct device_node *np, int *orientation)
> +{
> +	int rotation, ret;
> +
> +	ret = of_property_read_u32(np, "rotation", &rotation);
> +	if (ret == -EINVAL) {
> +		/* Don't return an error if there's no rotation property. */
> +		*orientation = DRM_MODE_PANEL_ORIENTATION_UNKNOWN;
> +		return 0;
> +	}
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	if (rotation == 0)
> +		*orientation = DRM_MODE_PANEL_ORIENTATION_NORMAL;
> +	else if (rotation == 90)
> +		*orientation = DRM_MODE_PANEL_ORIENTATION_RIGHT_UP;
> +	else if (rotation == 180)
> +		*orientation = DRM_MODE_PANEL_ORIENTATION_BOTTOM_UP;
> +	else if (rotation == 270)
> +		*orientation = DRM_MODE_PANEL_ORIENTATION_LEFT_UP;
> +	else
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(of_drm_get_panel_orientation);
>  #endif
>  
>  MODULE_AUTHOR("Thierry Reding <[email-masked]>");
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 8c738c0e6e9f..13631b2efbaa 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -197,11 +197,18 @@ int drm_panel_detach(struct drm_panel *panel);
>  
>  #if defined(CONFIG_OF) && defined(CONFIG_DRM_PANEL)
>  struct drm_panel *of_drm_find_panel(const struct device_node *np);
> +int of_drm_get_panel_orientation(const struct device_node *np,
> +				 int *orientation);
>  #else
>  static inline struct drm_panel *of_drm_find_panel(const struct device_node *np)
>  {
>  	return ERR_PTR(-ENODEV);
>  }
> +int of_drm_get_panel_orientation(const struct device_node *np,
> +				 int *orientation)
> +{
> +	return -ENODEV;
> +}
>  #endif
>  
>  #endif
> -- 
> 2.22.0.rc2.383.gf4fbbf30c2-goog

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