[PATCH] drm/fb-helper: Support deferred setup

[Maarten Lankhorst]

Op 28-06-17 om 13:32 schreef Daniel Vetter:
> FB helper code falls back to a 1024x768 mode if no outputs are connected
> or don't report back any modes upon initialization. This can be annoying
> because outputs that are added to FB helper later on can't be used with
> FB helper if they don't support a matching mode.
>
> The fallback is in place because VGA connectors can happen to report an
> unknown connection status even when they are in fact connected.
>
> Some drivers have custom solutions in place to defer FB helper setup
> until at least one output is connected. But the logic behind these
> solutions is always the same and there is nothing driver-specific about
> it, so a better alterative is to fix the FB helper core and add support
> for all drivers automatically.
>
> This patch adds support for deferred FB helper setup. It checks all the
> connectors for their connection status, and if all of them report to be
> disconnected marks the FB helper as needing deferred setup. Whet setup
> is deferred, the FB helper core will automatically retry setup after a
> hotplug event, and it will keep trying until it succeeds.
>
> v2: Rebase onto my entirely reworked fbdev helper locking. One big
> difference is that this version again drops&reacquires the fbdev lock
> (which is now fb_helper->lock, but before this patch series it was
> mode_config->mutex), because register_framebuffer must be able to
> recurse back into fbdev helper code for the initial screen setup.
>
> v3: __drm_fb_helper_initial_config must hold fb_helper->lock upon
> return, I've fumbled that in the deferred setup case (Liviu).
>
> v4: I was blind, redo this all. __drm_fb_helper_initial_config
> shouldn't need to reacquire fb_helper->lock, that just confuses
> callers. I myself got confused by kernel_fb_helper_lock and somehow
> thought it's the same as fb_helper->lock. Tsk.
>
> Also simplify the logic a bit (we don't need two functions to probe
> connectors), we can stick much closer to the existing code. And update
> some comments I've spotted that are outdated.
>
> v5: Don't pass -EAGAIN to drivers, it's just an internal error code
> (Liviu).
>
> Cc: Liviu Dudau <liviu at dudau.co.uk>
> Cc: John Stultz <john.stultz at linaro.org>
> Cc: Thierry Reding <treding at nvidia.com> (v1)
> Tested-by: John Stultz <john.stultz at linaro.org>
> Signed-off-by: Thierry Reding <treding at nvidia.com> (v1)
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 101 ++++++++++++++++++++++++++--------------
>  include/drm/drm_fb_helper.h     |  23 +++++++++
>  2 files changed, 89 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index bbd4c6d0378d..e49bae10f0ee 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -521,6 +521,9 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
>  	if (!drm_fbdev_emulation)
>  		return -ENODEV;
>  
> +	if (READ_ONCE(fb_helper->deferred_setup))
> +		return 0;
> +
>  	mutex_lock(&fb_helper->lock);
>  	ret = restore_fbdev_mode(fb_helper);
>  
> @@ -1695,8 +1698,7 @@ EXPORT_SYMBOL(drm_fb_helper_pan_display);
>  
>  /*
>   * Allocates the backing storage and sets up the fbdev info structure through
> - * the ->fb_probe callback and then registers the fbdev and sets up the panic
> - * notifier.
> + * the ->fb_probe callback.
>   */
>  static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>  					 int preferred_bpp)
> @@ -1794,13 +1796,8 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>  	}
>  
>  	if (crtc_count == 0 || sizes.fb_width == -1 || sizes.fb_height == -1) {
> -		/*
> -		 * hmm everyone went away - assume VGA cable just fell out
> -		 * and will come back later.
> -		 */
> -		DRM_INFO("Cannot find any crtc or sizes - going 1024x768\n");
> -		sizes.fb_width = sizes.surface_width = 1024;
> -		sizes.fb_height = sizes.surface_height = 768;
> +		DRM_INFO("Cannot find any crtc or sizes\n");
> +		return -EAGAIN;
>  	}
>  
>  	/* Handle our overallocation */
> @@ -2429,6 +2426,58 @@ static void drm_setup_crtcs(struct drm_fb_helper *fb_helper,
>  	kfree(enabled);
>  }
>  
> +/* Note: Drops fb_helper->lock before returning. */
> +static int __drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper,
> +					  int bpp_sel)
> +{
> +	struct drm_device *dev = fb_helper->dev;
> +	struct fb_info *info;
> +	unsigned int width, height;
> +	int ret;
> +
> +	width = dev->mode_config.max_width;
> +	height = dev->mode_config.max_height;
> +
> +	drm_setup_crtcs(fb_helper, width, height);
> +	ret = drm_fb_helper_single_fb_probe(fb_helper, bpp_sel);
> +	if (ret < 0) {
> +		if (ret == -EAGAIN) {
> +			fb_helper->preferred_bpp = bpp_sel;
> +			fb_helper->deferred_setup = true;
> +			ret = 0;
> +		}
> +		mutex_unlock(&fb_helper->lock);
> +
> +		return ret;
> +	}
> +
> +	fb_helper->deferred_setup = false;
> +
> +	info = fb_helper->fbdev;
> +	info->var.pixclock = 0;
> +
> +	/* Need to drop locks to avoid recursive deadlock in
> +	 * register_framebuffer. This is ok because the only thing left to do is
> +	 * register the fbdev emulation instance in kernel_fb_helper_list. */
> +	mutex_unlock(&fb_helper->lock);
> +
> +	ret = register_framebuffer(info);
> +	if (ret < 0)
> +		return ret;
> +
> +	dev_info(dev->dev, "fb%d: %s frame buffer device\n",
> +		 info->node, info->fix.id);
> +
> +	mutex_lock(&kernel_fb_helper_lock);
> +	if (list_empty(&kernel_fb_helper_list))
> +		register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
> +
> +	list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);
> +	mutex_unlock(&kernel_fb_helper_lock);
> +
> +	return 0;
> +}
> +
>  /**
>   * drm_fb_helper_initial_config - setup a sane initial connector configuration
>   * @fb_helper: fb_helper device struct
> @@ -2473,39 +2522,15 @@ static void drm_setup_crtcs(struct drm_fb_helper *fb_helper,
>   */
>  int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
>  {
> -	struct drm_device *dev = fb_helper->dev;
> -	struct fb_info *info;
>  	int ret;
>  
>  	if (!drm_fbdev_emulation)
>  		return 0;
>  
>  	mutex_lock(&fb_helper->lock);
> -	drm_setup_crtcs(fb_helper,
> -			dev->mode_config.max_width,
> -			dev->mode_config.max_height);
> -	ret = drm_fb_helper_single_fb_probe(fb_helper, bpp_sel);
> -	mutex_unlock(&fb_helper->lock);
> -	if (ret)
> -		return ret;
> +	ret = __drm_fb_helper_initial_config(fb_helper, bpp_sel);
>  
> -	info = fb_helper->fbdev;
> -	info->var.pixclock = 0;
> -	ret = register_framebuffer(info);
> -	if (ret < 0)
> -		return ret;
> -
> -	dev_info(dev->dev, "fb%d: %s frame buffer device\n",
> -		 info->node, info->fix.id);
> -
> -	mutex_lock(&kernel_fb_helper_lock);
> -	if (list_empty(&kernel_fb_helper_list))
> -		register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
> -
> -	list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);
> -	mutex_unlock(&kernel_fb_helper_lock);
> -
> -	return 0;
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_fb_helper_initial_config);
>  
> @@ -2538,6 +2563,12 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
>  		return 0;
>  
>  	mutex_lock(&fb_helper->lock);
> +	if (fb_helper->deferred_setup) {
> +		err = __drm_fb_helper_initial_config(fb_helper,
> +						     fb_helper->preferred_bpp);
Maybe rename this function to *_and_unlock? I had to read this code twice to make sure it works as intended. :)
> +		return err;
> +	}
> +
>  	if (!fb_helper->fb || !drm_fb_helper_is_bound(fb_helper)) {
>  		fb_helper->delayed_hotplug = true;
>  		mutex_unlock(&fb_helper->lock);
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index ea170b96e88d..a5ea6ffdfecc 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -232,6 +232,29 @@ struct drm_fb_helper {
>  	 * needs to be reprobe when fbdev is in control again.
>  	 */
>  	bool delayed_hotplug;
> +
> +	/**
> +	 * @deferred_setup:
> +	 *
> +	 * If no outputs are connected (disconnected or unknown) the FB helper
> +	 * code will defer setup until at least one of the outputs shows up.
> +	 * This field keeps track of the status so that setup can be retried
> +	 * at every hotplug event until it succeeds eventually.
> +	 *
> +	 * Protected by @lock.
> +	 */
> +	bool deferred_setup;
> +
> +	/**
> +	 * @preferred_bpp:
> +	 *
> +	 * Temporary storage for the driver's preferred BPP setting passed to
> +	 * FB helper initialization. This needs to be tracked so that deferred
> +	 * FB helper setup can pass this on.
> +	 *
> +	 * See also: @deferred_setup
> +	 */
> +	int preferred_bpp;
>  };
>  
>  /**