drm/i915: Implement blocking read for pipe CRC files

seq_file is not quite the right interface for these ones. We have a
circular buffer with a new entry per vblank on one side and a process
wanting to dequeue the CRC with a read().

It's quite racy to wait for vblank in user land and then try to read a
pipe_crc file, sometimes the CRC interrupt hasn't been fired and we end
up with an EOF.

So, let's have the read on the pipe_crc file block until the interrupt
gives us a new entry. At that point we can wake the reading process.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b201a214279e..b2be05791b2f 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1221,6 +1221,8 @@ static void ivb_pipe_crc_update(struct drm_device *dev, enum pipe pipe)
 
 	head = (head + 1) & (INTEL_PIPE_CRC_ENTRIES_NR - 1);
 	atomic_set(&pipe_crc->head, head);
+
+	wake_up_interruptible(&pipe_crc->wq);
 }
 #else
 static void ivb_pipe_crc_update(struct drm_device *dev, int pipe) {}