[PATCH 1/2] drm/amdgpu: add debugfs for reset registers list

[Sharma, Shashank]

Amar,
Apart from the long comment,there are a few more bugs in the patch, 
which I have mentioned here inline. Please check them out.

- Shashank

On 2/8/2022 9:18 AM, Christian König wrote:
> Am 08.02.22 um 09:16 schrieb Somalapuram Amaranath:
>> List of register to be populated for dump collection during the GPU 
>> reset.
>>
>> Signed-off-by: Somalapuram Amaranath <Amaranath.Somalapuram at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu.h         |  3 ++
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 60 +++++++++++++++++++++
>>   2 files changed, 63 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> index b85b67a88a3d..78fa46f959c5 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> @@ -1097,6 +1097,9 @@ struct amdgpu_device {
>>       struct amdgpu_reset_control     *reset_cntl;
>>       uint32_t                        
>> ip_versions[HW_ID_MAX][HWIP_MAX_INSTANCE];
>> +
>> +    /* reset dump register */
>> +    long            reset_dump_reg_list[128];
> 
> I don't have time for a full review, but using long here certainly makes 
> no sense.
> 
> long is either 32bit or 64bit depending on the CPU architecture.
> 
> Regards,
> Christian.
> 
>>   };
>>   static inline struct amdgpu_device *drm_to_adev(struct drm_device 
>> *ddev)
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> index 164d6a9e9fbb..dad268e8a81a 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> @@ -1609,6 +1609,64 @@ DEFINE_DEBUGFS_ATTRIBUTE(fops_ib_preempt, NULL,
>>   DEFINE_DEBUGFS_ATTRIBUTE(fops_sclk_set, NULL,
>>               amdgpu_debugfs_sclk_set, "%llu\n");
>> +static ssize_t amdgpu_reset_dump_register_list_read(struct file *f,
>> +                char __user *buf, size_t size, loff_t *pos)
>> +{
>> +    struct amdgpu_device *adev = (struct amdgpu_device 
>> *)file_inode(f)->i_private;
>> +    char *reg_offset;
>> +    int i, r, len;
>> +
>> +    reg_offset = kmalloc(2048, GFP_KERNEL);
>> +    memset(reg_offset,  0, 2048);
>> +    for (i = 0; adev->reset_dump_reg_list[i] != 0; i++)

This loop termination condition is incorrect, why are we running the 
loop until adev->reset_dump_reg_list[i] != 0 ?

What if I have 10 registers to dump, but my 4th register value is 0 ? It 
will break the loop at 4 and we will not get all values.

>> +        sprintf(reg_offset + strlen(reg_offset), "0x%lx ", 
>> adev->reset_dump_reg_list[i]);
>> +
>> +    sprintf(reg_offset + strlen(reg_offset), "\n");
>> +    len = strlen(reg_offset);
>> +
>> +    if (*pos >=  len)
>> +        return 0;
>> +
>> +    r = copy_to_user(buf, reg_offset, len);
>> +    *pos += len - r;
>> +    kfree(reg_offset);

Also, why are we doing a dynamic memory allocation for reg_offest ? We 
can simply use adev->reset_dump_reg_list[i] isnt't it ?

simply
for (i=0; i<num_of_regs;i++) {
	copy_to_user(buf, adev->reg_list[i], sizeof(uint64_t));
}

Or without even a loop, simply:
copy_to_user(buf, &adev->reg_list, num_regs * sizeof(uint64_t));

- Shashank

>> +
>> +    return len - r;
>> +}
>> +
>> +static ssize_t amdgpu_reset_dump_register_list_write(struct file *f, 
>> const char __user *buf,
>> +        size_t size, loff_t *pos)
>> +{
>> +    struct amdgpu_device *adev = (struct amdgpu_device 
>> *)file_inode(f)->i_private;
>> +    char *reg_offset, *reg;
>> +    int ret, i = 0;
>> +
>> +    reg_offset = kmalloc(size, GFP_KERNEL);
>> +    memset(reg_offset,  0, size);
>> +    ret = copy_from_user(reg_offset, buf, size);
>> +

We are not allowing user to write into the list, so this whole function 
can just be a NOOP.

- Shashank

>> +    if (ret)
>> +        return -EFAULT;
>> +
>> +    while ((reg = strsep(&reg_offset, " ")) != NULL) {
>> +        ret  = kstrtol(reg, 16, &adev->reset_dump_reg_list[i]);
>> +        if (ret)
>> +            return -EINVAL;
>> +        i++;
>> +    }
>> +
>> +    kfree(reg_offset);
>> +
>> +    return size;
>> +}
>> +
>> +static const struct file_operations amdgpu_reset_dump_register_list = {
>> +    .owner = THIS_MODULE,
>> +    .read = amdgpu_reset_dump_register_list_read,
>> +    .write = amdgpu_reset_dump_register_list_write,
>> +    .llseek = default_llseek
>> +};
>> +
>>   int amdgpu_debugfs_init(struct amdgpu_device *adev)
>>   {
>>       struct dentry *root = adev_to_drm(adev)->primary->debugfs_root;
>> @@ -1672,6 +1730,8 @@ int amdgpu_debugfs_init(struct amdgpu_device *adev)
>>                   &amdgpu_debugfs_test_ib_fops);
>>       debugfs_create_file("amdgpu_vm_info", 0444, root, adev,
>>                   &amdgpu_debugfs_vm_info_fops);
>> +    debugfs_create_file("amdgpu_reset_dump_register_list", 0644, 
>> root, adev,
>> +                &amdgpu_reset_dump_register_list);
>>       adev->debugfs_vbios_blob.data = adev->bios;
>>       adev->debugfs_vbios_blob.size = adev->bios_size;
>