drm/amdgpu: read reg in each iterator of psp_wait_for loop

v2: fix the SOS loading failure for PSP v3.1
Signed-off-by: Junwei Zhang <Jerry.Zhang@amd.com>
Cc: stable@vger.kernel.org
Acked-by: Alex Deucher <alexander.deucher@amd.com> (v1)
Acked-by: Huang Rui <ray.huang@amd.com> (v1)
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_psp.c

@@ -98,9 +98,8 @@ int psp_wait_for(struct psp_context *psp, uint32_t reg_index,
 	int i;
 	struct amdgpu_device *adev = psp->adev;
 
-	val = RREG32(reg_index);
-
 	for (i = 0; i < adev->usec_timeout; i++) {
+		val = RREG32(reg_index);
 		if (check_changed) {
 			if (val != reg_val)
 				return 0;

drivers/gpu/drm/amd/amdgpu/psp_v3_1.c

@@ -237,11 +237,9 @@ int psp_v3_1_bootloader_load_sos(struct psp_context *psp)
 
 	/* there might be handshake issue with hardware which needs delay */
 	mdelay(20);
-#if 0
 	ret = psp_wait_for(psp, SOC15_REG_OFFSET(MP0, 0, mmMP0_SMN_C2PMSG_81),
 			   RREG32_SOC15(MP0, 0, mmMP0_SMN_C2PMSG_81),
 			   0, true);
-#endif
 
 	return ret;
 }