[PATCH] drm/amdgpu: add mb for si

[Zhenneng Li]

During reboot test on arm64 platform, it may failure on boot,
so add this mb in smc.

The error message are as follows:
[    6.996395][ 7] [  T295] [drm:amdgpu_device_ip_late_init [amdgpu]] *ERROR*
			    late_init of IP block <si_dpm> failed -22
[    7.006919][ 7] [  T295] amdgpu 0000:04:00.0: amdgpu_device_ip_late_init failed
[    7.014224][ 7] [  T295] amdgpu 0000:04:00.0: Fatal error during GPU init

Signed-off-by: Zhenneng Li <lizhenneng at kylinos.cn>
---
 drivers/gpu/drm/amd/pm/legacy-dpm/si_smc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/amd/pm/legacy-dpm/si_smc.c b/drivers/gpu/drm/amd/pm/legacy-dpm/si_smc.c
index 8f994ffa9cd1..c7656f22278d 100644
--- a/drivers/gpu/drm/amd/pm/legacy-dpm/si_smc.c
+++ b/drivers/gpu/drm/amd/pm/legacy-dpm/si_smc.c
@@ -155,6 +155,8 @@ bool amdgpu_si_is_smc_running(struct amdgpu_device *adev)
 	u32 rst = RREG32_SMC(SMC_SYSCON_RESET_CNTL);
 	u32 clk = RREG32_SMC(SMC_SYSCON_CLOCK_CNTL_0);
 
+	mb();
+
 	if (!(rst & RST_REG) && !(clk & CK_DISABLE))
 		return true;
 
-- 
2.25.1