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author | 2013-11-03 20:46:34 +0100 | |
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committer | 2014-04-23 10:32:33 +0200 | |
commit | fc8fd40eb29a936cc689d0008863d39a67741c67 (patch) | |
tree | 708dadf9ad9eb22a9a88cf12de128501c63d731c /drivers/gpu/drm/i915/i915_dma.c | |
parent | drm: kill drm_bus->bus_type (diff) | |
download | linux-fc8fd40eb29a936cc689d0008863d39a67741c67.tar.gz linux-fc8fd40eb29a936cc689d0008863d39a67741c67.tar.bz2 linux-fc8fd40eb29a936cc689d0008863d39a67741c67.zip |
drm: Rip out totally bogus vga_switcheroo->can_switch locking
So I just wanted to add a new field to struct drm_device and
accidentally stumbled over something. According to comments
dev->open_count is protected by dev->count_lock, but that's totally
not the case. It's protected by drm_global_mutex.
Unfortunately the vga switcheroo callbacks took this comment at face
value. The problem is that we can't just take the drm_global_mutex
because:
- It would lead to a locking inversion with the driver load/unload
paths.
- It wouldn't actually protect anything, for that we'd need to wrap
the entire vga switcheroo code in the drm_global_mutex. And I'm not
sure whether that would actually solve anything.
What we probably want is a try_to_grab_switcheroo reference kind of
thing which is used in the driver's ->open callback. Then we could
move all that ->can_switch madness into the vga switcheroo core where
it really belongs.
But since that would amount to real work take the easy way out and
just add a comment. It's definitely not going to make anything worse
since doing switcheroo state changes while restarting X just isn't
recommended. Even though the delayed switching code does exactly that.
v2:
- Simplify the ->can_switch implementations more (Thierry)
- Fix comment about the dev->open_count locking (Thierry)
Cc: Thierry Reding <treding@nvidia.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> (v1)
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Diffstat (limited to 'drivers/gpu/drm/i915/i915_dma.c')
-rw-r--r-- | drivers/gpu/drm/i915/i915_dma.c | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c index 96177eec0a0e..283ff06001bc 100644 --- a/drivers/gpu/drm/i915/i915_dma.c +++ b/drivers/gpu/drm/i915/i915_dma.c @@ -1277,12 +1277,13 @@ static void i915_switcheroo_set_state(struct pci_dev *pdev, enum vga_switcheroo_ static bool i915_switcheroo_can_switch(struct pci_dev *pdev) { struct drm_device *dev = pci_get_drvdata(pdev); - bool can_switch; - spin_lock(&dev->count_lock); - can_switch = (dev->open_count == 0); - spin_unlock(&dev->count_lock); - return can_switch; + /* + * FIXME: open_count is protected by drm_global_mutex but that would lead to + * locking inversion with the driver load path. And the access here is + * completely racy anyway. So don't bother with locking for now. + */ + return dev->open_count == 0; } static const struct vga_switcheroo_client_ops i915_switcheroo_ops = { |