drm/i915: Fail to load driver if KMS request without GEM

The i915's implementation of KMS requires GEM in order to manage the
memory and execution domains of the framebuffer and associated
resources. By the point at which we detect broken a BIOS and need to
disable GEM, we have already registered ourselves as a KMS driver with
several subsystems. Rather than introducing a fragile unwind and attempt
to continue with UMS, spit out an error and unload the driver.

References:

  [Bug 15754] IP: [<ffffffffa0207589>] drm_mm_search_free+0x49/0x90 [drm]
              BUG: unable to handle kernel NULL pointer dereference at (null)
  https://bugzilla.kernel.org/show_bug.cgi?id=15754

[drm:i915_driver_load] *ERROR* Detected broken video BIOS with
262140/262144kB of video memory stolen.
[drm:i915_driver_load] *ERROR* Disabling GEM. (try reducing stolen
memory or updating the BIOS to fix).
i915 0000:00:02.0: irq 30 for MSI/MSI-X
[drm] set up 255M of stolen space
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffffa0207589>] drm_mm_search_free+0x49/0x90 [drm]
PGD 69719067 PUD 69dda067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
last sysfs file: /sys/module/snd_seq_oss/initstate
CPU 1
Pid: 867, comm: modprobe Not tainted 2.6.33-ARCH #1 G43Twins-FullHD/To
Be Filled By O.E.M.
RIP: 0010:[<ffffffffa0207589>]  [<ffffffffa0207589>] drm_mm_search_free+0x49/0x90 [drm]
RSP: 0018:ffff8800699f3af8  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffffffffffffff RCX: 0000000000000000
RDX: 0000000000001000 RSI: 0000000000001000 RDI: ffff8800693d0f78
RBP: ffff8800699f3b18 R08: 0000000000001000 R09: 0000000000000000
R10: 2222222222222222 R11: 0000000000000000 R12: ffff880068de70c0
R13: 0000000000001000 R14: 0000000000000000 R15: ffff8800689cb000
FS:  00007fa93f4e5700(0000) GS:ffff880001880000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000695a0000 CR4: 00000000000406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process modprobe (pid: 867, threadinfo ffff8800699f2000, task ffff8800694f4740)
Stack:
 ffff880068de73c0 ffff880068de70c0 ffff8800689cb000 0000000000001000
<0> ffff8800699f3b68 ffffffffa0299f63 ffff8800693d0f78 0000120068de70c0
<0> ffff8800689cb000 ffff880068de73c0 ffff880068de70c0 ffff8800689cb000
Call Trace:
 [<ffffffffa0299f63>] i915_gem_object_bind_to_gtt+0x83/0x360 [i915]
 [<ffffffffa029a2e5>] i915_gem_object_pin+0xa5/0xb0 [i915]
 [<ffffffffa029a3c5>] i915_gem_init_ringbuffer+0xd5/0x510 [i915]
 [<ffffffffa028dbee>] i915_driver_load+0x4ce/0xd00 [i915]
 [<ffffffffa0205d37>] ? drm_sysfs_device_add+0x87/0xb0 [drm]
 [<ffffffffa0203363>] ? drm_get_minor+0x1d3/0x330 [drm]
 [<ffffffffa02037e6>] drm_get_dev+0x326/0x580 [drm]
 [<ffffffffa02bc0a5>] i915_pci_probe+0x10/0xd0 [i915]
 [<ffffffff811e98a2>] local_pci_probe+0x12/0x20
 [<ffffffff811ea8e0>] pci_device_probe+0x80/0xb0
 [<ffffffff8127b12a>] ? driver_sysfs_add+0x5a/0x90
 [<ffffffff8127b273>] driver_probe_device+0x93/0x1a0
 [<ffffffff8127b413>] __driver_attach+0x93/0xa0
 [<ffffffff8127b380>] ? __driver_attach+0x0/0xa0
 [<ffffffff8127a8f8>] bus_for_each_dev+0x68/0x90
 [<ffffffff8127b0c9>] driver_attach+0x19/0x20
 [<ffffffff8127a0ad>] bus_add_driver+0xcd/0x2d0
 [<ffffffff8127b718>] driver_register+0x78/0x140
 [<ffffffff811eab91>] __pci_register_driver+0x51/0xd0
 [<ffffffffa02d6000>] ? i915_init+0x0/0x52 [i915]
 [<ffffffffa01fdc31>] drm_init+0x111/0x120 [drm]
 [<ffffffff810eb0cd>] ? register_shrinker+0x4d/0x60
 [<ffffffffa02d6000>] ? i915_init+0x0/0x52 [i915]
 [<ffffffffa02d6050>] i915_init+0x50/0x52 [i915]
 [<ffffffff81002047>] do_one_initcall+0x37/0x1a0
 [<ffffffff8108ed17>] sys_init_module+0xd7/0x250
 [<ffffffff81009fc2>] system_call_fastpath+0x16/0x1b
Code: eb 29 49 8b 41 28 31 d2 49 f7 f5 85 d2 74 39 44 89 c0 29 d0 48 89 c2 48 01 f2 49 39 d2 73 29 0f 1f 00 49 89 da 4c 89 d3 4d 89 d9 <4d> 8b 19 49 39 f9 41 0f 18 0b 74 2b 4d 8b 51 30 4d 89 cc 49 39
RIP  [<ffffffffa0207589>] drm_mm_search_free+0x49/0x90 [drm]
 RSP <ffff8800699f3af8>
CR2: 0000000000000000

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_dma.c

@@ -1672,6 +1672,13 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 		dev_priv->has_gem = 0;
 	}
 
+	if (dev_priv->has_gem == 0 &&
+	    drm_core_check_feature(dev, DRIVER_MODESET)) {
+		DRM_ERROR("kernel modesetting requires GEM, disabling driver.\n");
+		ret = -ENODEV;
+		goto out_iomapfree;
+	}
+
 	dev->driver->get_vblank_counter = i915_get_vblank_counter;
 	dev->max_vblank_count = 0xffffff; /* only 24 bits of frame count */
 	if (IS_G4X(dev) || IS_IRONLAKE(dev) || IS_GEN6(dev)) {