[PATCH v2 4/8] v4l: vsp1: Use reference counting for fragments

[Kieran Bingham]

Extend the display list body with a reference count, allowing bodies to
be kept as long as a reference is maintained. This provides the ability
to keep a cached copy of bodies which will not change, so that they can
be re-applied to multiple display lists.

Signed-off-by: Kieran Bingham <kieran.bingham+rene...@ideasonboard.com>

---
This could be squashed into the fragment update code, but it's not a
straightforward squash as the refcounts will affect both:
  v4l: vsp1: Provide a fragment pool
and
  v4l: vsp1: Convert display lists to use new fragment pool
therefore, I have kept this separate to prevent breaking bisectability
of the vsp-tests.
---
 drivers/media/platform/vsp1/vsp1_clu.c |  7 ++++++-
 drivers/media/platform/vsp1/vsp1_dl.c  | 15 ++++++++++++++-
 drivers/media/platform/vsp1/vsp1_lut.c |  7 ++++++-
 3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/vsp1/vsp1_clu.c 
b/drivers/media/platform/vsp1/vsp1_clu.c
index 52c523625e2f..175717018e11 100644
--- a/drivers/media/platform/vsp1/vsp1_clu.c
+++ b/drivers/media/platform/vsp1/vsp1_clu.c
@@ -257,8 +257,13 @@ static void clu_configure(struct vsp1_entity *entity,
                clu->clu = NULL;
                spin_unlock_irqrestore(&clu->lock, flags);
 
-               if (dlb)
+               if (dlb) {
                        vsp1_dl_list_add_fragment(dl, dlb);
+
+                       /* release our local reference */
+                       vsp1_dl_fragment_put(dlb);
+               }
+
                break;
        }
 }
diff --git a/drivers/media/platform/vsp1/vsp1_dl.c 
b/drivers/media/platform/vsp1/vsp1_dl.c
index 6ffdc3549283..37feda248946 100644
--- a/drivers/media/platform/vsp1/vsp1_dl.c
+++ b/drivers/media/platform/vsp1/vsp1_dl.c
@@ -14,6 +14,7 @@
 #include <linux/device.h>
 #include <linux/dma-mapping.h>
 #include <linux/gfp.h>
+#include <linux/refcount.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 
@@ -58,6 +59,8 @@ struct vsp1_dl_body {
        struct list_head list;
        struct list_head free;
 
+       refcount_t refcnt;
+
        struct vsp1_dl_fragment_pool *pool;
        struct vsp1_device *vsp1;
 
@@ -230,6 +233,7 @@ struct vsp1_dl_body *vsp1_dl_fragment_get(struct 
vsp1_dl_fragment_pool *pool)
        if (!list_empty(&pool->free)) {
                dlb = list_first_entry(&pool->free, struct vsp1_dl_body, free);
                list_del(&dlb->free);
+               refcount_set(&dlb->refcnt, 1);
        }
 
        spin_unlock_irqrestore(&pool->lock, flags);
@@ -244,6 +248,9 @@ void vsp1_dl_fragment_put(struct vsp1_dl_body *dlb)
        if (!dlb)
                return;
 
+       if (!refcount_dec_and_test(&dlb->refcnt))
+               return;
+
        dlb->num_entries = 0;
 
        spin_lock_irqsave(&dlb->pool->lock, flags);
@@ -428,7 +435,11 @@ void vsp1_dl_list_write(struct vsp1_dl_list *dl, u32 reg, 
u32 data)
  * list, in the order in which fragments are added.
  *
  * Adding a fragment to a display list passes ownership of the fragment to the
- * list. The caller must not touch the fragment after this call.
+ * list. The caller must not modify the fragment after this call, but can 
retain
+ * a reference to it for future use if necessary, to add to subsequent lists.
+ *
+ * The reference count of the body is incremented by this attachment, and thus
+ * the caller should release it's reference if does not want to cache the body.
  *
  * Fragments are only usable for display lists in header mode. Attempt to
  * add a fragment to a header-less display list will return an error.
@@ -440,6 +451,8 @@ int vsp1_dl_list_add_fragment(struct vsp1_dl_list *dl,
        if (dl->dlm->mode != VSP1_DL_MODE_HEADER)
                return -EINVAL;
 
+       refcount_inc(&dlb->refcnt);
+
        list_add_tail(&dlb->list, &dl->fragments);
        return 0;
 }
diff --git a/drivers/media/platform/vsp1/vsp1_lut.c 
b/drivers/media/platform/vsp1/vsp1_lut.c
index 57482e057e54..388bd89ade0b 100644
--- a/drivers/media/platform/vsp1/vsp1_lut.c
+++ b/drivers/media/platform/vsp1/vsp1_lut.c
@@ -213,8 +213,13 @@ static void lut_configure(struct vsp1_entity *entity,
                lut->lut = NULL;
                spin_unlock_irqrestore(&lut->lock, flags);
 
-               if (dlb)
+               if (dlb) {
                        vsp1_dl_list_add_fragment(dl, dlb);
+
+                       /* release our local reference */
+                       vsp1_dl_fragment_put(dlb);
+               }
+
                break;
        }
 }
-- 
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