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			We need to hold the dev->mode_config.mutex whilst detecting the output status. But we also need to drop it for the call into drm_fb_helper_single_fb_probe(), which indirectly acquires the lock when attaching the fbcon. Failure to do so exposes a race with normal output probing. Detected by adding some warnings that the mutex is held to the backend detect routines: [ 17.772456] WARNING: at drivers/gpu/drm/i915/intel_crt.c:471 intel_crt_detect+0x3e/0x373 [i915]() [ 17.772458] Hardware name: Latitude E6400 [ 17.772460] Modules linked in: .... [ 17.772582] Pid: 11, comm: kworker/0:1 Tainted: G W 2.6.38.4-custom.2 #8 [ 17.772584] Call Trace: [ 17.772591] [<ffffffff81046af5>] ? warn_slowpath_common+0x78/0x8c [ 17.772603] [<ffffffffa03f3e5c>] ? intel_crt_detect+0x3e/0x373 [i915] [ 17.772612] [<ffffffffa0355d49>] ? drm_helper_probe_single_connector_modes+0xbf/0x2af [drm_kms_helper] [ 17.772619] [<ffffffffa03534d5>] ? drm_fb_helper_probe_connector_modes+0x39/0x4d [drm_kms_helper] [ 17.772625] [<ffffffffa0354760>] ? drm_fb_helper_hotplug_event+0xa5/0xc3 [drm_kms_helper] [ 17.772633] [<ffffffffa035577f>] ? output_poll_execute+0x146/0x17c [drm_kms_helper] [ 17.772638] [<ffffffff81193c01>] ? cfq_init_queue+0x247/0x345 [ 17.772644] [<ffffffffa0355639>] ? output_poll_execute+0x0/0x17c [drm_kms_helper] [ 17.772648] [<ffffffff8105b540>] ? process_one_work+0x193/0x28e [ 17.772652] [<ffffffff8105c6bc>] ? worker_thread+0xef/0x172 [ 17.772655] [<ffffffff8105c5cd>] ? worker_thread+0x0/0x172 [ 17.772658] [<ffffffff8105c5cd>] ? worker_thread+0x0/0x172 [ 17.772663] [<ffffffff8105f767>] ? kthread+0x7a/0x82 [ 17.772668] [<ffffffff8100a724>] ? kernel_thread_helper+0x4/0x10 [ 17.772671] [<ffffffff8105f6ed>] ? kthread+0x0/0x82 [ 17.772674] [<ffffffff8100a720>] ? kernel_thread_helper+0x0/0x10 Reported-by: Frederik Himpe <fhimpe@telenet.be> References: https://bugs.freedesktop.org/show_bug.cgi?id=36394 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Dave Airlie <airlied@redhat.com>
		
			
				
	
	
		
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| /*
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|  * Copyright (c) 2006-2009 Red Hat Inc.
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|  * Copyright (c) 2006-2008 Intel Corporation
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|  * Copyright (c) 2007 Dave Airlie <airlied@linux.ie>
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|  *
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|  * DRM framebuffer helper functions
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|  *
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|  * Permission to use, copy, modify, distribute, and sell this software and its
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|  * documentation for any purpose is hereby granted without fee, provided that
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|  * the above copyright notice appear in all copies and that both that copyright
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|  * notice and this permission notice appear in supporting documentation, and
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|  * that the name of the copyright holders not be used in advertising or
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|  * publicity pertaining to distribution of the software without specific,
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|  * written prior permission.  The copyright holders make no representations
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|  * about the suitability of this software for any purpose.  It is provided "as
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|  * is" without express or implied warranty.
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|  *
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|  * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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|  * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
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|  * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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|  * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
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|  * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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|  * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
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|  * OF THIS SOFTWARE.
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|  *
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|  * Authors:
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|  *      Dave Airlie <airlied@linux.ie>
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|  *      Jesse Barnes <jesse.barnes@intel.com>
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|  */
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| #ifndef DRM_FB_HELPER_H
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| #define DRM_FB_HELPER_H
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| 
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| struct drm_fb_helper;
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| 
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| #include <linux/kgdb.h>
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| 
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| struct drm_fb_helper_crtc {
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| 	uint32_t crtc_id;
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| 	struct drm_mode_set mode_set;
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| 	struct drm_display_mode *desired_mode;
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| };
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| 
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| struct drm_fb_helper_surface_size {
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| 	u32 fb_width;
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| 	u32 fb_height;
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| 	u32 surface_width;
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| 	u32 surface_height;
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| 	u32 surface_bpp;
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| 	u32 surface_depth;
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| };
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| 
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| struct drm_fb_helper_funcs {
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| 	void (*gamma_set)(struct drm_crtc *crtc, u16 red, u16 green,
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| 			  u16 blue, int regno);
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| 	void (*gamma_get)(struct drm_crtc *crtc, u16 *red, u16 *green,
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| 			  u16 *blue, int regno);
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| 
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| 	int (*fb_probe)(struct drm_fb_helper *helper,
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| 			struct drm_fb_helper_surface_size *sizes);
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| };
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| 
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| struct drm_fb_helper_connector {
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| 	struct drm_connector *connector;
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| 	struct drm_cmdline_mode cmdline_mode;
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| };
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| 
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| struct drm_fb_helper {
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| 	struct drm_framebuffer *fb;
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| 	struct drm_framebuffer *saved_fb;
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| 	struct drm_device *dev;
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| 	struct drm_display_mode *mode;
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| 	int crtc_count;
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| 	struct drm_fb_helper_crtc *crtc_info;
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| 	int connector_count;
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| 	struct drm_fb_helper_connector **connector_info;
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| 	struct drm_fb_helper_funcs *funcs;
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| 	int conn_limit;
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| 	struct fb_info *fbdev;
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| 	u32 pseudo_palette[17];
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| 	struct list_head kernel_fb_list;
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| 
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| 	/* we got a hotplug but fbdev wasn't running the console
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| 	   delay until next set_par */
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| 	bool delayed_hotplug;
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| };
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| 
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| int drm_fb_helper_single_fb_probe(struct drm_fb_helper *helper,
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| 				  int preferred_bpp);
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| 
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| int drm_fb_helper_init(struct drm_device *dev,
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| 		       struct drm_fb_helper *helper, int crtc_count,
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| 		       int max_conn);
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| void drm_fb_helper_fini(struct drm_fb_helper *helper);
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| int drm_fb_helper_blank(int blank, struct fb_info *info);
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| int drm_fb_helper_pan_display(struct fb_var_screeninfo *var,
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| 			      struct fb_info *info);
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| int drm_fb_helper_set_par(struct fb_info *info);
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| int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
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| 			    struct fb_info *info);
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| int drm_fb_helper_setcolreg(unsigned regno,
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| 			    unsigned red,
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| 			    unsigned green,
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| 			    unsigned blue,
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| 			    unsigned transp,
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| 			    struct fb_info *info);
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| 
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| bool drm_fb_helper_restore_fbdev_mode(struct drm_fb_helper *fb_helper);
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| void drm_fb_helper_restore(void);
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| void drm_fb_helper_fill_var(struct fb_info *info, struct drm_fb_helper *fb_helper,
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| 			    uint32_t fb_width, uint32_t fb_height);
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| void drm_fb_helper_fill_fix(struct fb_info *info, uint32_t pitch,
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| 			    uint32_t depth);
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| 
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| int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
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| 
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| int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
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| bool drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
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| int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
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| int drm_fb_helper_debug_enter(struct fb_info *info);
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| int drm_fb_helper_debug_leave(struct fb_info *info);
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| 
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| #endif
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