drm/i915: Use a spin lock to protect the pipe crc struct

Daniel pointed out that it was hard to get anything lockless to work
correctly, so don't even try for this non critical piece of code and
just use a spin lock.

v2: Make intel_pipe_crc->opened a bool
v3: Use assert_spin_locked() instead of a comment (Daniel Vetter)
v4: Use spin_lock_irq() in the debugfs functions (they can only be
    called from process context),
    Use spin_lock() in the pipe_crc_update() function that can only be
    called from an interrupt handler,
    Use wait_event_interruptible_lock_irq() when waiting for data in the
    cicular buffer to ensure proper locking around the condition we are
    waiting for. (Daniel Vetter)

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2e1e884ac86c..5bfcf0f91a51 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1249,10 +1249,11 @@ struct intel_pipe_crc_entry {
 
 #define INTEL_PIPE_CRC_ENTRIES_NR	128
 struct intel_pipe_crc {
-	atomic_t available;		/* exclusive access to the device */
+	spinlock_t lock;
+	bool opened;		/* exclusive access to the result file */
 	struct intel_pipe_crc_entry *entries;
 	enum intel_pipe_crc_source source;
-	atomic_t head, tail;
+	int head, tail;
 	wait_queue_head_t wq;
 };