drm/shmem-helper: Add and use pages_pin_count

Add separate pages_pin_count for tracking of whether drm-shmem pages are
moveable or not. With the addition of memory shrinker support to drm-shmem,
the pages_use_count will no longer determine whether pages are hard-pinned
in memory, but whether pages exist and are soft-pinned (and could be swapped
out). The pages_pin_count > 1 will hard-pin pages in memory.

Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.d>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250322212608.40511-8-dmitry.osipenko@collabora.com

2 files changed, 26 insertions, 1 deletions

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 277e792a0c5c..d338b36f4eaa 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -177,6 +177,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 			drm_gem_shmem_put_pages_locked(shmem);
 
 		drm_WARN_ON(obj->dev, shmem->pages_use_count);
+		drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count));
 
 		dma_resv_unlock(shmem->base.resv);
 	}
@@ -257,7 +258,12 @@ int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(shmem->base.dev, drm_gem_is_imported(&shmem->base));
 
+	if (refcount_inc_not_zero(&shmem->pages_pin_count))
+		return 0;
+
 	ret = drm_gem_shmem_get_pages_locked(shmem);
+	if (!ret)
+		refcount_set(&shmem->pages_pin_count, 1);
 
 	return ret;
 }
@@ -267,7 +273,8 @@ void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
 {
 	dma_resv_assert_held(shmem->base.resv);
 
-	drm_gem_shmem_put_pages_locked(shmem);
+	if (refcount_dec_and_test(&shmem->pages_pin_count))
+		drm_gem_shmem_put_pages_locked(shmem);
 }
 EXPORT_SYMBOL(drm_gem_shmem_unpin_locked);
 
@@ -288,6 +295,9 @@ int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(obj->dev, drm_gem_is_imported(obj));
 
+	if (refcount_inc_not_zero(&shmem->pages_pin_count))
+		return 0;
+
 	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
 	if (ret)
 		return ret;
@@ -311,6 +321,9 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(obj->dev, drm_gem_is_imported(obj));
 
+	if (refcount_dec_not_one(&shmem->pages_pin_count))
+		return;
+
 	dma_resv_lock(shmem->base.resv, NULL);
 	drm_gem_shmem_unpin_locked(shmem);
 	dma_resv_unlock(shmem->base.resv);
@@ -660,6 +673,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
 	if (drm_gem_is_imported(&shmem->base))
 		return;
 
+	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", shmem->pages_use_count);
 	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
 	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 0609e336479d..d411215fe494 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -40,6 +40,17 @@ struct drm_gem_shmem_object {
 	unsigned int pages_use_count;
 
 	/**
+	 * @pages_pin_count:
+	 *
+	 * Reference count on the pinned pages table.
+	 *
+	 * Pages are hard-pinned and reside in memory if count
+	 * greater than zero. Otherwise, when count is zero, the pages are
+	 * allowed to be evicted and purged by memory shrinker.
+	 */
+	refcount_t pages_pin_count;
+
+	/**
 	 * @madv: State for madvise
 	 *
 	 * 0 is active/inuse.