drm/amdgpu/virt: add function to check MMIO (v2)

MMIO space can be blocked on virtualised device. Add this
function to check if MMIO is blocked or not.

Todo: need a reliable method such like communation
with hypervisor.

v2:
 - add comments inline
Signed-off-by: pding <Pixel.Ding@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -24,6 +24,14 @@
 #include "amdgpu.h"
 #define MAX_KIQ_REG_WAIT	100000000 /* in usecs */
 
+bool amdgpu_virt_mmio_blocked(struct amdgpu_device *adev)
+{
+	/* By now all MMIO pages except mailbox are blocked */
+	/* if blocking is enabled in hypervisor. Choose the */
+	/* SCRATCH_REG0 to test. */
+	return RREG32_NO_KIQ(0xc040) == 0xffffffff;
+}
+
 int amdgpu_allocate_static_csa(struct amdgpu_device *adev)
 {
 	int r;

drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h

@@ -276,6 +276,7 @@ static inline bool is_virtual_machine(void)
 }
 
 struct amdgpu_vm;
+bool amdgpu_virt_mmio_blocked(struct amdgpu_device *adev);
 int amdgpu_allocate_static_csa(struct amdgpu_device *adev);
 int amdgpu_map_static_csa(struct amdgpu_device *adev, struct amdgpu_vm *vm,
 			  struct amdgpu_bo_va **bo_va);