Re: [PATCH v2 4/4] drm/fb-helper: improve documentation and print warnings

[Daniel Vetter]

On Fri, Sep 07, 2018 at 12:18:10AM +0200, Peter Wu wrote:
> Clarify the relation between drm_fb_helper_fbdev_setup/teardown. Clarify
> requirements for the new generic fbdev emulation API and log some more
> details in case the driver does something wrong. Fix related typos.
> 
> Cc: Noralf Trønnes <noralf@xxxxxxxxxxx>
> Signed-off-by: Peter Wu <peter@xxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 4b0dd20bccb8..7f92ff173986 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -2821,7 +2821,9 @@ EXPORT_SYMBOL(drm_fb_helper_hotplug_event);
>   * The caller must to provide a &drm_fb_helper_funcs->fb_probe callback
>   * function.
>   *
> - * See also: drm_fb_helper_initial_config()
> + * Use drm_fb_helper_fbdev_teardown() to destroy the fbdev.
> + *
> + * See also: drm_fb_helper_initial_config(), drm_fbdev_generic_setup().
>   *
>   * Returns:
>   * Zero on success or negative error code on failure.
> @@ -3037,7 +3039,7 @@ static struct fb_deferred_io drm_fbdev_defio = {
>   * @fb_helper: fbdev helper structure
>   * @sizes: describes fbdev size and scanout surface size
>   *
> - * This function uses the client API to crate a framebuffer backed by a dumb buffer.
> + * This function uses the client API to create a framebuffer backed by a dumb buffer.
>   *
>   * The _sys_ versions are used for &fb_ops.fb_read, fb_write, fb_fillrect,
>   * fb_copyarea, fb_imageblit.
> @@ -3165,8 +3167,10 @@ static int drm_fbdev_client_hotplug(struct drm_client_dev *client)
>  	if (dev->fb_helper)
>  		return drm_fb_helper_hotplug_event(dev->fb_helper);
>  
> -	if (!dev->mode_config.num_connector)
> +	if (!dev->mode_config.num_connector) {
> +		DRM_DEV_DEBUG(dev->dev, "No connectors found, will not create framebuffer!\n");
>  		return 0;
> +	}
>  
>  	ret = drm_fb_helper_fbdev_setup(dev, fb_helper, &drm_fb_helper_generic_funcs,
>  					fb_helper->preferred_bpp, 0);
> @@ -3187,13 +3191,15 @@ static const struct drm_client_funcs drm_fbdev_client_funcs = {
>  };
>  
>  /**
> - * drm_fb_helper_generic_fbdev_setup() - Setup generic fbdev emulation
> + * drm_fbdev_generic_setup() - Setup generic fbdev emulation

Hm, drm_fb_helper_ would be the OCD prefix we use everywhere, but better
to make the docs match the code. Feel free to throw a rename patch on top.

>   * @dev: DRM device
>   * @preferred_bpp: Preferred bits per pixel for the device.
>   *                 @dev->mode_config.preferred_depth is used if this is zero.
>   *
>   * This function sets up generic fbdev emulation for drivers that supports
> - * dumb buffers with a virtual address and that can be mmap'ed.
> + * dumb buffers with a virtual address and that can be mmap'ed. If the driver
> + * does not support these functions, it could use drm_fb_helper_fbdev_setup().
> + * This function can only be used with devices created using drm_dev_register().

This last line is misleading, since every drm device is called with
drm_dev_register(). It's just not all called by driver code directly.
With this line removed:

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

I'll leave it to Gerd to apply this all.
-Daniel


>   *
>   * Restore, hotplug events and teardown are all taken care of. Drivers that do
>   * suspend/resume need to call drm_fb_helper_set_suspend_unlocked() themselves.
> @@ -3206,6 +3212,8 @@ static const struct drm_client_funcs drm_fbdev_client_funcs = {
>   * This function is safe to call even when there are no connectors present.
>   * Setup will be retried on the next hotplug event.
>   *
> + * The fbdev is destroyed by drm_dev_unregister().
> + *
>   * Returns:
>   * Zero on success or negative error code on failure.
>   */
> @@ -3214,6 +3222,8 @@ int drm_fbdev_generic_setup(struct drm_device *dev, unsigned int preferred_bpp)
>  	struct drm_fb_helper *fb_helper;
>  	int ret;
>  
> +	WARN(dev->fb_helper, "fb_helper is already set!\n");
> +
>  	if (!drm_fbdev_emulation)
>  		return 0;
>  
> @@ -3224,12 +3234,15 @@ int drm_fbdev_generic_setup(struct drm_device *dev, unsigned int preferred_bpp)
>  	ret = drm_client_new(dev, &fb_helper->client, "fbdev", &drm_fbdev_client_funcs);
>  	if (ret) {
>  		kfree(fb_helper);
> +		DRM_DEV_ERROR(dev->dev, "Failed to register client: %d\n", ret);
>  		return ret;
>  	}
>  
>  	fb_helper->preferred_bpp = preferred_bpp;
>  
> -	drm_fbdev_client_hotplug(&fb_helper->client);
> +	ret = drm_fbdev_client_hotplug(&fb_helper->client);
> +	if (ret)
> +		DRM_DEV_DEBUG(dev->dev, "client hotplug ret=%d\n", ret);
>  
>  	return 0;
>  }
> -- 
> 2.18.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch