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

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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@xxxxxxx>

- 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@xxxxxxx>
---
  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;




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