[Nouveau] [PATCH] drm/nouveau: handle same-fb page flips

[Marcin Slusarz]

It's questionable use case, but weston/wayland already relies on this behaviour,
and other drivers don't care about it, so it's a matter of compatibility.
Without it, process invoking such page flip hangs in unkillable state, trying
to reserve the same buffer twice.

Signed-off-by: Marcin Slusarz <marcin.slus...@gmail.com>
---
 drivers/gpu/drm/nouveau/nouveau_display.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c 
b/drivers/gpu/drm/nouveau/nouveau_display.c
index 61f370d..a52cfd3 100644
--- a/drivers/gpu/drm/nouveau/nouveau_display.c
+++ b/drivers/gpu/drm/nouveau/nouveau_display.c
@@ -530,9 +530,11 @@ nouveau_page_flip_reserve(struct nouveau_bo *old_bo,
        if (ret)
                goto fail;
 
-       ret = ttm_bo_reserve(&old_bo->bo, false, false, false, 0);
-       if (ret)
-               goto fail_unreserve;
+       if (likely(old_bo != new_bo)) {
+               ret = ttm_bo_reserve(&old_bo->bo, false, false, false, 0);
+               if (ret)
+                       goto fail_unreserve;
+       }
 
        return 0;
 
@@ -551,8 +553,10 @@ nouveau_page_flip_unreserve(struct nouveau_bo *old_bo,
        nouveau_bo_fence(new_bo, fence);
        ttm_bo_unreserve(&new_bo->bo);
 
-       nouveau_bo_fence(old_bo, fence);
-       ttm_bo_unreserve(&old_bo->bo);
+       if (likely(old_bo != new_bo)) {
+               nouveau_bo_fence(old_bo, fence);
+               ttm_bo_unreserve(&old_bo->bo);
+       }
 
        nouveau_bo_unpin(old_bo);
 }
@@ -624,6 +628,12 @@ nouveau_crtc_page_flip(struct drm_crtc *crtc, struct 
drm_framebuffer *fb,
        if (!drm->channel)
                return -ENODEV;
 
+       if (unlikely(old_bo == new_bo)) {
+               char name[sizeof(current->comm)];
+               pr_debug_ratelimited("'%s': useless page flip invoked\n",
+                               get_task_comm(name, current));
+       }
+
        s = kzalloc(sizeof(*s), GFP_KERNEL);
        if (!s)
                return -ENOMEM;
-- 
1.7.12

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