diff --git a/drivers/gpu/drm/radeon/r100.c b/drivers/gpu/drm/radeon/r100.c
index ae4c857..8ff7cac 100644
--- a/drivers/gpu/drm/radeon/r100.c
+++ b/drivers/gpu/drm/radeon/r100.c
@@ -4141,8 +4141,15 @@
 	if (reg < rdev->rmmio_size && !always_indirect)
 		return readl(((void __iomem *)rdev->rmmio) + reg);
 	else {
+		unsigned long flags;
+		uint32_t ret;
+
+		spin_lock_irqsave(&rdev->mmio_idx_lock, flags);
 		writel(reg, ((void __iomem *)rdev->rmmio) + RADEON_MM_INDEX);
-		return readl(((void __iomem *)rdev->rmmio) + RADEON_MM_DATA);
+		ret = readl(((void __iomem *)rdev->rmmio) + RADEON_MM_DATA);
+		spin_unlock_irqrestore(&rdev->mmio_idx_lock, flags);
+
+		return ret;
 	}
 }
 
@@ -4152,8 +4159,12 @@
 	if (reg < rdev->rmmio_size && !always_indirect)
 		writel(v, ((void __iomem *)rdev->rmmio) + reg);
 	else {
+		unsigned long flags;
+
+		spin_lock_irqsave(&rdev->mmio_idx_lock, flags);
 		writel(reg, ((void __iomem *)rdev->rmmio) + RADEON_MM_INDEX);
 		writel(v, ((void __iomem *)rdev->rmmio) + RADEON_MM_DATA);
+		spin_unlock_irqrestore(&rdev->mmio_idx_lock, flags);
 	}
 }
 
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 609bb18..285fb3f 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -1556,6 +1556,8 @@
 	/* Register mmio */
 	resource_size_t			rmmio_base;
 	resource_size_t			rmmio_size;
+	/* protects concurrent MM_INDEX/DATA based register access */
+	spinlock_t mmio_idx_lock;
 	void __iomem			*rmmio;
 	radeon_rreg_t			mc_rreg;
 	radeon_wreg_t			mc_wreg;
diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
index e2f5f88..49b0659 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -1059,6 +1059,7 @@
 
 	/* Registers mapping */
 	/* TODO: block userspace mapping of io register */
+	spin_lock_init(&rdev->mmio_idx_lock);
 	rdev->rmmio_base = pci_resource_start(rdev->pdev, 2);
 	rdev->rmmio_size = pci_resource_len(rdev->pdev, 2);
 	rdev->rmmio = ioremap(rdev->rmmio_base, rdev->rmmio_size);