[PATCH] drm/nouveau/nvif: fix null ptr deref on pre-fermi boards

[Ben Skeggs]

Check that gpfifo.post() exists before trying to call it.

Fixes: 862450a85b85 ("drm/nouveau/gf100-: track chan progress with non-WFI semaphore release")
Reported-by: Jamie Heilman <jamie at audible.transient.net>
Reported-by: Rui Salvaterra <rsalvaterra at gmail.com>
Tested-by: Rui Salvaterra <rsalvaterra at gmail.com>
Signed-off-by: Ben Skeggs <bskeggs at nvidia.com>
---
 drivers/gpu/drm/nouveau/nvif/chan.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nvif/chan.c b/drivers/gpu/drm/nouveau/nvif/chan.c
index baa10227d51a..80c01017d642 100644
--- a/drivers/gpu/drm/nouveau/nvif/chan.c
+++ b/drivers/gpu/drm/nouveau/nvif/chan.c
@@ -39,6 +39,9 @@ nvif_chan_gpfifo_post(struct nvif_chan *chan)
 	const u32 pbptr = (chan->push.cur - map) + chan->func->gpfifo.post_size;
 	const u32 gpptr = (chan->gpfifo.cur + 1) & chan->gpfifo.max;
 
+	if (!chan->func->gpfifo.post)
+		return 0;
+
 	return chan->func->gpfifo.post(chan, gpptr, pbptr);
 }
 
-- 
2.49.0