On Tue, Apr 22, 2014 at 10:45:19PM +0200, Daniel Vetter wrote: > 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@xxxxxxxxxx> > Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> (v1) > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > --- > drivers/gpu/drm/i915/i915_dma.c | 11 ++++++----- > drivers/gpu/drm/nouveau/nouveau_vga.c | 11 ++++++----- > drivers/gpu/drm/radeon/radeon_device.c | 11 ++++++----- > include/drm/drmP.h | 2 +- > 4 files changed, 19 insertions(+), 16 deletions(-) Looks good: Reviewed-by: Thierry Reding <treding@xxxxxxxxxx>
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