[Bug 29140] [rs690] Freeze at Xorg startup when using KMS and multiple screens

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https://bugs.freedesktop.org/show_bug.cgi?id=29140

--- Comment #9 from steckdenis@yahoo.fr 2010-08-12 09:57:45 PDT ---
Hello,

I think I found the problem, but I am unfortunately unable to fix it (I don't
know the radeon module enough).

A change between the 2.6.34 and 2.6.35 kernels added a bunch of functions in
drivers/gpu/drm/radeon/radeon_pm.c. The function that causes troubles to me is
radeon_pm_set_clocks(struct radeon_device *rdev); .

This function begins by locking three mutexes, including rdev->cp.mutex.

My card is a r300, so the code goes through the "else" branch of the if. This
branch contains a call to radeon_fence_emit.

Now in radeon_fence.c . I don't know how, but this function happens to call
radeon_fence_wait. The problem is that radeon_fence_wait calls
r300_gpu_is_lockup, by branching in "if
(unlikely(!radeon_fence_signaled(fence))) {".

In r300.c : r300_gpu_is_lockup, called by radeon_fence_wait, calls
radeon_ring_lock, because it wants to write in the ring.

In radeon_ring.c : radeon_ring_lock begins by calling
"mutex_lock(&rdev->cp.mutex);", the exact same mutex as the one already locked
by radeon_pm_set_clocks. That seems to be the problem.

Cheers.

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