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drm: Avoid drm_global_mutex for simple inc/dec of dev->open_count

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Since drm_global_mutex is a true global mutex across devices, we don't
want to acquire it unless absolutely necessary. For maintaining the
device local open_count, we can use atomic operations on the counter
itself, except when making the transition to/from 0. Here, we tackle the
easy portion of delaying acquiring the drm_global_mutex for the final
release by using atomic_dec_and_mutex_lock(), leaving the global
serialisation across the device opens.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Thomas Hellström (VMware) <thomas_os@shipmail.org>
Reviewed-by: Thomas Hellström <thellstrom@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200124130107.125404-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson
2020-01-24 13:01:07 +00:00
parent 7a2c65dd32
commit 7e13ad8964
6 changed files with 13 additions and 13 deletions
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2
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
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@@ -1137,7 +1137,7 @@ static bool amdgpu_switcheroo_can_switch(struct pci_dev *pdev)
* 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;
return atomic_read(&dev->open_count) == 0;
}
static const struct vga_switcheroo_client_ops amdgpu_switcheroo_ops = {