drm/i915: Keep the CRC values into a circular buffer

There are a few good properties to a circular buffer, for instance it
has a number of entries (before we were always dumping the full buffer).

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

1 files changed, 15 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index d2074f129a36..73d76af13ed4 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -30,6 +30,7 @@
 
 #include <linux/sysrq.h>
 #include <linux/slab.h>
+#include <linux/circ_buf.h>
 #include <drm/drmP.h>
 #include <drm/i915_drm.h>
 #include "i915_drv.h"
@@ -1195,20 +1196,30 @@ static void ivb_pipe_crc_update(struct drm_device *dev, enum pipe pipe)
         struct intel_pipe_crc *pipe_crc = &dev_priv->pipe_crc[pipe];
         struct intel_pipe_crc_entry *entry;
         ktime_t now;
-        int ts, slot;
+        int ts, head, tail;
+
+        head = atomic_read(&pipe_crc->head);
+        tail = atomic_read(&pipe_crc->tail);
+
+        if (CIRC_SPACE(head, tail, INTEL_PIPE_CRC_ENTRIES_NR) < 1) {
+                DRM_ERROR("CRC buffer overflowing\n");
+                return;
+        }
+
+        entry = &pipe_crc->entries[head];
 
         now = ktime_get();
         ts = ktime_to_us(now);
 
-        slot = (atomic_read(&pipe_crc->slot) + 1) % INTEL_PIPE_CRC_ENTRIES_NR;
-        entry = &pipe_crc->entries[slot];
         entry->timestamp = ts;
         entry->crc[0] = I915_READ(PIPE_CRC_RES_1_IVB(pipe));
         entry->crc[1] = I915_READ(PIPE_CRC_RES_2_IVB(pipe));
         entry->crc[2] = I915_READ(PIPE_CRC_RES_3_IVB(pipe));
         entry->crc[3] = I915_READ(PIPE_CRC_RES_4_IVB(pipe));
         entry->crc[4] = I915_READ(PIPE_CRC_RES_5_IVB(pipe));
-        atomic_set(&dev_priv->pipe_crc[pipe].slot, slot);
+
+        head = (head + 1) & (INTEL_PIPE_CRC_ENTRIES_NR - 1);
+        atomic_set(&pipe_crc->head, head);
 }
 #else
 static void ivb_pipe_crc_update(struct drm_device *dev, int pipe) {}