[PATCH] drm: Rip out totally bogus vga_switcheroo->can_switch locking
Thierry Reding
thierry.reding at gmail.com
Wed Apr 23 00:28:55 PDT 2014
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 at nvidia.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com> (v1)
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
> 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 at nvidia.com>
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