drm/amdgpu: implement mmio byte access helper for MB

mailbox registers can be accessed with a byte boundry according
to BIF team, so this patch prepares register byte access
and will be used by following patches.

Actually, for mailbox registers once the byte field is touched even not changed,
the mailbox behaves, so we need the byte width accessing to those sort of regs.
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Pixel Ding <Pixel.Ding@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1632,6 +1632,9 @@ uint32_t amdgpu_mm_rreg(struct amdgpu_device *adev, uint32_t reg,
 			uint32_t acc_flags);
 void amdgpu_mm_wreg(struct amdgpu_device *adev, uint32_t reg, uint32_t v,
 		    uint32_t acc_flags);
+void amdgpu_mm_wreg8(struct amdgpu_device *adev, uint32_t offset, uint8_t value);
+uint8_t amdgpu_mm_rreg8(struct amdgpu_device *adev, uint32_t offset);
+
 u32 amdgpu_io_rreg(struct amdgpu_device *adev, u32 reg);
 void amdgpu_io_wreg(struct amdgpu_device *adev, u32 reg, u32 v);
 
@@ -1655,6 +1658,9 @@ int emu_soc_asic_init(struct amdgpu_device *adev);
 #define RREG32_NO_KIQ(reg) amdgpu_mm_rreg(adev, (reg), AMDGPU_REGS_NO_KIQ)
 #define WREG32_NO_KIQ(reg, v) amdgpu_mm_wreg(adev, (reg), (v), AMDGPU_REGS_NO_KIQ)
 
+#define RREG8(reg) amdgpu_mm_rreg8(adev, (reg))
+#define WREG8(reg, v) amdgpu_mm_wreg8(adev, (reg), (v))
+
 #define RREG32(reg) amdgpu_mm_rreg(adev, (reg), 0)
 #define RREG32_IDX(reg) amdgpu_mm_rreg(adev, (reg), AMDGPU_REGS_IDX)
 #define DREG32(reg) printk(KERN_INFO "REGISTER: " #reg " : 0x%08X\n", amdgpu_mm_rreg(adev, (reg), 0))

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

@@ -121,6 +121,32 @@ uint32_t amdgpu_mm_rreg(struct amdgpu_device *adev, uint32_t reg,
 	return ret;
 }
 
+/*
+ * MMIO register read with bytes helper functions
+ * @offset:bytes offset from MMIO start
+ *
+*/
+
+uint8_t amdgpu_mm_rreg8(struct amdgpu_device *adev, uint32_t offset) {
+	if (offset < adev->rmmio_size)
+		return (readb(adev->rmmio + offset));
+	BUG();
+}
+
+/*
+ * MMIO register write with bytes helper functions
+ * @offset:bytes offset from MMIO start
+ * @value: the value want to be written to the register
+ *
+*/
+void amdgpu_mm_wreg8(struct amdgpu_device *adev, uint32_t offset, uint8_t value) {
+	if (offset < adev->rmmio_size)
+		writeb(value, adev->rmmio + offset);
+	else
+		BUG();
+}
+
+
 void amdgpu_mm_wreg(struct amdgpu_device *adev, uint32_t reg, uint32_t v,
 		    uint32_t acc_flags)
 {