tu: Add a "scratch bo" allocation mechanism

This is simpler than a full-blown memory reuse mechanism, but is good
enough to make sure that repeatedly doing a copy that requires the
linear staging buffer workaround won't use excessive memory or be slowed
down due to repeated allocations.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5007>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/freedreno/vulkan/tu_private.h b/src/freedreno/vulkan/tu_private.h
index 99da10a568b..1c32e60000a 100644
--- a/src/freedreno/vulkan/tu_private.h
+++ b/src/freedreno/vulkan/tu_private.h
@@ -509,6 +509,17 @@ struct tu_device
    uint32_t vsc_draw_strm_pitch;
    uint32_t vsc_prim_strm_pitch;
 
+#define MIN_SCRATCH_BO_SIZE_LOG2 12 /* A page */
+
+   /* Currently the kernel driver uses a 32-bit GPU address space, but it
+    * should be impossible to go beyond 48 bits.
+    */
+   struct {
+      struct tu_bo bo;
+      mtx_t construct_mtx;
+      bool initialized;
+   } scratch_bos[48 - MIN_SCRATCH_BO_SIZE_LOG2];
+
    struct tu_bo border_color;
 
    struct list_head shader_slabs;
@@ -531,6 +542,15 @@ tu_bo_finish(struct tu_device *dev, struct tu_bo *bo);
 VkResult
 tu_bo_map(struct tu_device *dev, struct tu_bo *bo);
 
+/* Get a scratch bo for use inside a command buffer. This will always return
+ * the same bo given the same size or similar sizes, so only one scratch bo
+ * can be used at the same time. It's meant for short-lived things where we
+ * need to write to some piece of memory, read from it, and then immediately
+ * discard it.
+ */
+VkResult
+tu_get_scratch_bo(struct tu_device *dev, uint64_t size, struct tu_bo **bo);
+
 struct tu_cs_entry
 {
    /* No ownership */