[PATCH v16 14/20] drm/shmem-helper: Use refcount_t for vmap_use_count

[Dmitry Osipenko]

Use refcount_t helper for vmap_use_count to make refcounting consistent
with pages_use_count and pages_pin_count that use refcount_t. This will
allow to optimize unlocked vmappings by skipping reservation locking if
refcnt > 1 and also makes vmapping to benefit from the refcount_t's
overflow checks.

Suggested-by: Boris Brezillon <boris.brezil...@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 28 +++++++++++---------------
 include/drm/drm_gem_shmem_helper.h     |  2 +-
 2 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c 
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 899f655a65bb..4633a418faba 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -144,7 +144,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
        } else if (!shmem->imported_sgt) {
                dma_resv_lock(shmem->base.resv, NULL);
 
-               drm_WARN_ON(obj->dev, shmem->vmap_use_count);
+               drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
 
                if (shmem->sgt) {
                        dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
@@ -345,23 +345,25 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object 
*shmem,
 
                dma_resv_assert_held(shmem->base.resv);
 
-               if (shmem->vmap_use_count++ > 0) {
+               if (refcount_inc_not_zero(&shmem->vmap_use_count)) {
                        iosys_map_set_vaddr(map, shmem->vaddr);
                        return 0;
                }
 
                ret = drm_gem_shmem_pin_locked(shmem);
                if (ret)
-                       goto err_zero_use;
+                       return ret;
 
                if (shmem->map_wc)
                        prot = pgprot_writecombine(prot);
                shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
                                    VM_MAP, prot);
-               if (!shmem->vaddr)
+               if (!shmem->vaddr) {
                        ret = -ENOMEM;
-               else
+               } else {
                        iosys_map_set_vaddr(map, shmem->vaddr);
+                       refcount_set(&shmem->vmap_use_count, 1);
+               }
        }
 
        if (ret) {
@@ -374,8 +376,6 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object 
*shmem,
 err_put_pages:
        if (!obj->import_attach)
                drm_gem_shmem_unpin_locked(shmem);
-err_zero_use:
-       shmem->vmap_use_count = 0;
 
        return ret;
 }
@@ -403,14 +403,10 @@ void drm_gem_shmem_vunmap_locked(struct 
drm_gem_shmem_object *shmem,
        } else {
                dma_resv_assert_held(shmem->base.resv);
 
-               if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
-                       return;
-
-               if (--shmem->vmap_use_count > 0)
-                       return;
-
-               vunmap(shmem->vaddr);
-               drm_gem_shmem_unpin_locked(shmem);
+               if (refcount_dec_and_test(&shmem->vmap_use_count)) {
+                       vunmap(shmem->vaddr);
+                       drm_gem_shmem_unpin_locked(shmem);
+               }
        }
 
        shmem->vaddr = NULL;
@@ -656,7 +652,7 @@ void drm_gem_shmem_print_info(const struct 
drm_gem_shmem_object *shmem,
 
        drm_printf_indent(p, indent, "pages_pin_count=%u\n", 
refcount_read(&shmem->pages_pin_count));
        drm_printf_indent(p, indent, "pages_use_count=%u\n", 
refcount_read(&shmem->pages_use_count));
-       drm_printf_indent(p, indent, "vmap_use_count=%u\n", 
shmem->vmap_use_count);
+       drm_printf_indent(p, indent, "vmap_use_count=%u\n", 
refcount_read(&shmem->vmap_use_count));
        drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_print_info);
diff --git a/include/drm/drm_gem_shmem_helper.h 
b/include/drm/drm_gem_shmem_helper.h
index 396958a98c34..63e91e8f2d5c 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -81,7 +81,7 @@ struct drm_gem_shmem_object {
         * Reference count on the virtual address.
         * The address are un-mapped when the count reaches zero.
         */
-       unsigned int vmap_use_count;
+       refcount_t vmap_use_count;
 
        /**
         * @got_pages_sgt:
-- 
2.41.0