[PATCH 4.9 30/86] drm/amdkfd: Fix SDMA ring buffer size calculation

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: shaoyunl <Shaoyun.Liu@xxxxxxx>


[ Upstream commit d12fb13f23199faa7e536acec1db49068e5a067d ]

ffs function return the position of the first bit set on 1 based.
(bit zero returns 1).

Signed-off-by: shaoyun liu <shaoyun.liu@xxxxxxx>
Signed-off-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Reviewed-by: Oded Gabbay <oded.gabbay@xxxxxxxxx>
Signed-off-by: Oded Gabbay <oded.gabbay@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c
@@ -215,8 +215,8 @@ static int update_mqd_sdma(struct mqd_ma
 	BUG_ON(!mm || !mqd || !q);
 
 	m = get_sdma_mqd(mqd);
-	m->sdma_rlc_rb_cntl = ffs(q->queue_size / sizeof(unsigned int)) <<
-			SDMA0_RLC0_RB_CNTL__RB_SIZE__SHIFT |
+	m->sdma_rlc_rb_cntl = (ffs(q->queue_size / sizeof(unsigned int)) - 1)
+			<< SDMA0_RLC0_RB_CNTL__RB_SIZE__SHIFT |
 			q->vmid << SDMA0_RLC0_RB_CNTL__RB_VMID__SHIFT |
 			1 << SDMA0_RLC0_RB_CNTL__RPTR_WRITEBACK_ENABLE__SHIFT |
 			6 << SDMA0_RLC0_RB_CNTL__RPTR_WRITEBACK_TIMER__SHIFT;