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

["Sharma, Shashank" <shashank.sharma@amd.com>]

Based on confirmation from Christian, it seems my understanding of the 
design was not correct, and user must add a list of registers to dump.

That resolves most of my comments automatically, @Amar, please fix a max 
register condition in the loop, to handle the negative testing case and 
the uint32_t stuff. With those two changes in place, feel free to use 
for this patch:

Reviewed-by: Shashank Sharma <shashank.sharma@amd.com>

- Shashank

On 2/8/2022 3:31 PM, Sharma, Shashank wrote:
>  >> User only update the list of reg offsets on init, there is no
>  >> predefined reg offset from kernel code.
> 
> I missed this comment in the last patch, and this makes me a bit 
> confused. During the design phase, did we agree to have this whole list 
> loaded from user ? which means that if user doesn't define the list at 
> init, we will not send the trace_event().
> 
> Or was it kernel has a list, and user can modify if he wants to, and we 
> will dump the values as per the register list.
> 
> @Christian ?
> 
> Regards
> Shashank
> On 2/8/2022 3:18 PM, Sharma, Shashank wrote:
>>
>>
>> On 2/8/2022 2:39 PM, Somalapuram, Amaranath wrote:
>>>
>>>
>>> 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.
>>
>> Pls see my comment in the end.
>>
>>>> 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);
>>
>> We also want to understand how does the value 2048 came into picture, 
>> probably a macro which calculates the size preprocessing time will 
>> work better.
>>
>> #define #define N_REGS_DUMP_GPU_RESET 10
>> #define BUFFER_SZ(N_REGS_DUMP_GPU_RESET * (sizeof uint64_t) + 1)
>>
>> This first macro can be used later for the loop count for registers as 
>> well.
>>
>>>>>> +    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
>>
>> Not by the cost of logic of course :).
>>
>> Now you can run this loop here.
>>
>> for (i = 0; i < N_REGS...; i++) {
>>      register_value_copy_here;
>> }
>>
>>>>>> +        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)
>>>
>>
>> We are just adding 0x in front of the reg value, so honestly I don't 
>> see a huge improvement in the user readability, but if you still want 
>> to do the dynamic allocation of memory, add the register offset or 
>> name as well, I mean then it should read like:
>>
>> 0x1234 = 0xABCD
>> 0x1238 = 0xFFFF
>>
>> - 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
>>> 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;
>>>>>