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>

3 files changed, 29 insertions, 14 deletions

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 0d8a9a397a24..991abff94e1e 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -27,6 +27,7 @@
  */
 
 #include <linux/seq_file.h>
+#include <linux/circ_buf.h>
 #include <linux/ctype.h>
 #include <linux/debugfs.h>
 #include <linux/slab.h>
@@ -1739,25 +1740,28 @@ static int i915_pipe_crc(struct seq_file *m, void *data)
         struct drm_device *dev = node->minor->dev;
         struct drm_i915_private *dev_priv = dev->dev_private;
         enum pipe pipe = (enum pipe)node->info_ent->data;
-        const struct intel_pipe_crc *pipe_crc = &dev_priv->pipe_crc[pipe];
-        int i;
-        int start;
+        struct intel_pipe_crc *pipe_crc = &dev_priv->pipe_crc[pipe];
+        int head, tail;
 
         if (dev_priv->pipe_crc[pipe].source == INTEL_PIPE_CRC_SOURCE_NONE) {
                 seq_puts(m, "none\n");
                 return 0;
         }
 
-        start = atomic_read(&pipe_crc->slot) + 1;
         seq_puts(m, " timestamp     CRC1     CRC2     CRC3     CRC4     CRC5\n");
-        for (i = 0; i < INTEL_PIPE_CRC_ENTRIES_NR; i++) {
-                const struct intel_pipe_crc_entry *entry =
-                        &pipe_crc->entries[(start + i) %
-                                           INTEL_PIPE_CRC_ENTRIES_NR];
+        head = atomic_read(&pipe_crc->head);
+        tail = atomic_read(&pipe_crc->tail);
+
+        while (CIRC_CNT(head, tail, INTEL_PIPE_CRC_ENTRIES_NR) >= 1) {
+                struct intel_pipe_crc_entry *entry = &pipe_crc->entries[tail];
 
                 seq_printf(m, "%12u %8x %8x %8x %8x %8x\n", entry->timestamp,
                            entry->crc[0], entry->crc[1], entry->crc[2],
                            entry->crc[3], entry->crc[4]);
+
+                BUILD_BUG_ON_NOT_POWER_OF_2(INTEL_PIPE_CRC_ENTRIES_NR);
+                tail = (tail + 1) & (INTEL_PIPE_CRC_ENTRIES_NR - 1);
+                atomic_set(&pipe_crc->tail, tail);
         }
 
         return 0;
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index bfaaaaee8a5b..a29a4a1d300a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1230,11 +1230,11 @@ struct intel_pipe_crc_entry {
         uint32_t crc[5];
 };
 
-#define INTEL_PIPE_CRC_ENTRIES_NR       200
+#define INTEL_PIPE_CRC_ENTRIES_NR       128
 struct intel_pipe_crc {
         struct intel_pipe_crc_entry entries[INTEL_PIPE_CRC_ENTRIES_NR];
         enum intel_pipe_crc_source source;
-        atomic_t slot;
+        atomic_t head, tail;
 };
 
 typedef struct drm_i915_private {
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) {}