From 8da032ade43def402501595401d4af3f27dfbe1f Mon Sep 17 00:00:00 2001
From: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Date: Fri, 4 Aug 2023 11:16:41 +0530
Subject: drm/amdgpu: Use READ_ONCE() when reading the values in
'sdma_v4_4_2_ring_get_rptr'
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Git-commit: bf227a4f0558320513b86c279996021480f9e750
Patch-mainline: v6.7-rc1
References: jsc#PED-3527 jsc#PED-5475 jsc#PED-6068 jsc#PED-6070 jsc#PED-6116 jsc#PED-6120 jsc#PED-5065 jsc#PED-5477 jsc#PED-5511 jsc#PED-6041 jsc#PED-6069 jsc#PED-6071
Use READ_ONCE() instead of declaring the pointer volatile. To prevent
the compiler from refetching or reordering the read, so that the read
value is always consistent.
Link: https://lwn.net/Articles/624126/
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Guchun Chen <guchun.chen@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: Le Ma <le.ma@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Le Ma <le.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c b/drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c
index f413898dda37..267c1b7b8dcd 100644
--- a/drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c
+++ b/drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c
@@ -154,13 +154,13 @@ static int sdma_v4_4_2_init_microcode(struct amdgpu_device *adev)
*/
static uint64_t sdma_v4_4_2_ring_get_rptr(struct amdgpu_ring *ring)
{
- u64 *rptr;
+ u64 rptr;
/* XXX check if swapping is necessary on BE */
- rptr = ((u64 *)&ring->adev->wb.wb[ring->rptr_offs]);
+ rptr = READ_ONCE(*((u64 *)&ring->adev->wb.wb[ring->rptr_offs]));
- DRM_DEBUG("rptr before shift == 0x%016llx\n", *rptr);
- return ((*rptr) >> 2);
+ DRM_DEBUG("rptr before shift == 0x%016llx\n", rptr);
+ return rptr >> 2;
}
/**
--
2.43.0