[PATCH] drm/amdgpu: Fix cat debugfs amdgpu_regs_didt causes kernel null pointer

[Lu Yao]

For 'AMDGPU_FAMILY_SI' family cards, in 'si_common_early_init' func, init
'didt_rreg' and 'didt_wreg' to 'NULL'. But in func
'amdgpu_debugfs_regs_didt_read/write', using 'RREG32_DIDT' 'WREG32_DIDT'
lacks of relevant judgment. And other 'amdgpu_ip_block_version' that use
these two definitions won't be added for 'AMDGPU_FAMILY_SI'.

So, add null pointer judgment before calling.

Signed-off-by: Lu Yao <yaolu@xxxxxxxxxx>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
index a53f436fa9f1..797d7d3bfd50 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
@@ -638,6 +638,11 @@ static ssize_t amdgpu_debugfs_regs_didt_read(struct file *f, char __user *buf,
 	if (size & 0x3 || *pos & 0x3)
 		return -EINVAL;
 
+	if (adev->didt_rreg == NULL) {
+		dev_err(adev->dev, "%s adev->didt_rreg is null!\n", __FUNC__);
+		return -EPERM;
+	}
+
 	r = pm_runtime_get_sync(adev_to_drm(adev)->dev);
 	if (r < 0) {
 		pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
@@ -694,6 +699,11 @@ static ssize_t amdgpu_debugfs_regs_didt_write(struct file *f, const char __user
 	if (size & 0x3 || *pos & 0x3)
 		return -EINVAL;
 
+	if (adev->didt_wreg == NULL) {
+		dev_err(adev->dev, "%s adev->didt_wreg is null!\n", __FUNC__);
+		return -EPERM;
+	}
+
 	r = pm_runtime_get_sync(adev_to_drm(adev)->dev);
 	if (r < 0) {
 		pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
-- 
2.25.1