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

["Somalapuram, Amaranath" <asomalap@amd.com>]

On 2/8/2022 4:43 PM, Sharma, Shashank wrote:
> I thought we spoke and agreed about:
> - Not doing dynamic memory allocation during a reset call,
as there is a redesign debugfs call will happen during the application 
initialization and not during reset.
> - Not doing string operations, but just dumping register values by index.
I think your referring to the second patch which happens during reset 
and no string operation in second patch.
> NACK !
>
> - 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@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.
>>
will change uint32_t.
>>>   };
>>>   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.
>
agreed, i try to avoid one more variable in adev
>>> +        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

it will not be in user readable format for debugfs, (if non readable is 
acceptable I will change this)

> +
>>>
>>> +    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
User only update the list of reg offsets on init, there is no predefined 
reg offset from kernel code.
>
>>> +    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;
>>