From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH 1/2] drm/i915: make backlight functions take
 a connector v3
Date: Fri, 11 Oct 2013 23:31:10 +0200
Message-ID: <20131011213110.GJ8303@phenom.ffwll.local>
References: <1381516314-6007-1-git-send-email-jbarnes@virtuousgeek.org>
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To: Jesse Barnes <jbarnes@virtuousgeek.org>
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On Fri, Oct 11, 2013 at 11:31:53AM -0700, Jesse Barnes wrote:

[snip]

>  static int intel_panel_get_brightness(struct backlight_device *bd)
>  {
> -	struct drm_device *dev = bl_get_data(bd);
> -	return intel_panel_get_backlight(dev);
> +	struct intel_connector *connector = bl_get_data(bd);
> +	struct drm_device *dev = connector->base.dev;
> +	enum pipe pipe;
> +	int ret = 0;
> +
> +	mutex_lock(&dev->mode_config.mutex);
> +	pipe = intel_get_pipe_from_connector(connector);
> +	mutex_unlock(&dev->mode_config.mutex);
> +	if (pipe == INVALID_PIPE) {
> +		ret = 0;
> +		goto out_unlock;
> +	}
> +
> +	ret = intel_panel_get_backlight(connector->base.dev, pipe);
> +out_unlock:
> +	mutex_unlock(&dev->mode_config.mutex);

I see mutex_unlock(&dev->mode_config.mutex) twice here. I think you've
just volunteered yourselve for some testcases ;-)

Ideas:
- Make sure all lvds/edp connectors are enabled and bash on all backlight
  interfaces (with igt_fork it's easy to do that concurrently).
- Race the above with output changes: dpms on/off and changing the crtc
  around.
- Race the above with system suspend for bonus points (can be completely
  stitched together from igt helpers).

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch