Re: [PATCH] drm/amdgpu: fix sysfs_emit/sysfs_emit_at warnings

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 08.09.21 um 12:22 schrieb Lazar, Lijo:
> On 9/8/2021 3:08 PM, Christian König wrote:
>> Am 08.09.21 um 11:29 schrieb Lazar, Lijo:
>>> On 9/8/2021 2:32 PM, Yu, Lang wrote:
>>>> [AMD Official Use Only]
>>>>> -----Original Message-----
>>>>> From: Lazar, Lijo <Lijo.Lazar@amd.com>
>>>>> Sent: Wednesday, September 8, 2021 4:55 PM
>>>>> To: Yu, Lang <Lang.Yu@amd.com>; Christian König
>>>>> <ckoenig.leichtzumerken@gmail.com>; amd-gfx@lists.freedesktop.org
>>>>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Huang, Ray
>>>>> <Ray.Huang@amd.com>; Tian Tao <tiantao6@hisilicon.com>
>>>>> Subject: Re: [PATCH] drm/amdgpu: fix sysfs_emit/sysfs_emit_at 
>>>>> warnings
>>>>>
>>>>>
>>>>>
>>>>> On 9/8/2021 1:14 PM, Yu, Lang wrote:
>>>>>> [AMD Official Use Only]
>>>>>>
>>>>>>
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: Lazar, Lijo <Lijo.Lazar@amd.com>
>>>>>>> Sent: Wednesday, September 8, 2021 3:36 PM
>>>>>>> To: Christian König <ckoenig.leichtzumerken@gmail.com>; Yu, Lang
>>>>>>> <Lang.Yu@amd.com>; amd-gfx@lists.freedesktop.org
>>>>>>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Huang, Ray
>>>>>>> <Ray.Huang@amd.com>; Tian Tao <tiantao6@hisilicon.com>
>>>>>>> Subject: Re: [PATCH] drm/amdgpu: fix sysfs_emit/sysfs_emit_at
>>>>>>> warnings
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 9/8/2021 12:07 PM, Christian König wrote:
>>>>>>>> Am 08.09.21 um 07:56 schrieb Lang Yu:
>>>>>>>>> sysfs_emit and sysfs_emit_at requrie a page boundary aligned buf
>>>>>>>>> address. Make them happy!
>>>>>>>>>
>>>>>>>>> Warning Log:
>>>>>>>>> [  492.545174] invalid sysfs_emit_at: buf:00000000f19bdfde at:0 [
>>>>>>>>> 492.546416] WARNING: CPU: 7 PID: 1304 at fs/sysfs/file.c:765
>>>>>>>>> sysfs_emit_at+0x4a/0xa0
>>>>>>>>> [  492.654805] Call Trace:
>>>>>>>>> [  492.655353]  ? smu_cmn_get_metrics_table+0x40/0x50 [amdgpu] [
>>>>>>>>> 492.656780]  vangogh_print_clk_levels+0x369/0x410 [amdgpu] [
>>>>>>>>> 492.658245] vangogh_common_print_clk_levels+0x77/0x80 [amdgpu] [
>>>>>>>>> 492.659733]  ? preempt_schedule_common+0x18/0x30 [ 492.660713]
>>>>>>>>> smu_print_ppclk_levels+0x65/0x90 [amdgpu] [ 492.662107]
>>>>>>>>> amdgpu_get_pp_od_clk_voltage+0x13d/0x190 [amdgpu] [ 492.663620]
>>>>>>>>> dev_attr_show+0x1d/0x40
>>>>>>>>
>>>>>>>> Mhm, that at least partially doesn't looks like the right 
>>>>>>>> approach to me.
>>>>>>>>
>>>>>>>> Why do we have string printing and sysfs code in the hardware
>>>>>>>> version specific backend in the first place?
>>>>>>>>
>>>>>>>
>>>>>>> This is a callback meant for printing ASIC specific information to
>>>>>>> sysfs node. The buffer passed in sysfs read is passed as it is 
>>>>>>> to the callback API.
>>>>>>>
>>>>>>>> That stuff needs to be implemented for each hardware generation 
>>>>>>>> and
>>>>>>>> is now cluttered with sysfs buffer offset calculations.
>>>>>>>>
>>>>>>>
>>>>>>> Looks like the warning happened because of this usage.
>>>>>>>
>>>>>>>                   size = amdgpu_dpm_print_clock_levels(adev, 
>>>>>>> OD_SCLK, buf);
>>>>>>>                   size += amdgpu_dpm_print_clock_levels(adev, 
>>>>>>> OD_MCLK,
>>>>>>> buf+size);
>>>>>>>                   size += amdgpu_dpm_print_clock_levels(adev,
>>>>>>> OD_VDDC_CURVE, buf+size);
>>>>>>>                   size += amdgpu_dpm_print_clock_levels(adev,
>>>>>>> OD_VDDGFX_OFFSET, buf+size);
>>>>>>>                   size += amdgpu_dpm_print_clock_levels(adev,
>>>>>>> OD_RANGE,
>>>>>>> buf+size);
>>>>>>>                   size += amdgpu_dpm_print_clock_levels(adev, 
>>>>>>> OD_CCLK,
>>>>>>> buf+size);
>>>>>>>
>>>>>>>
>>>>>> [Yu, Lang]
>>>>>> Yes. So it is fine we just fix the caller 
>>>>>> amdgpu_get_pp_od_clk_voltage like
>>>>> following:
>>>>>>
>>>>>> static ssize_t amdgpu_get_pp_od_clk_voltage(struct device *dev,
>>>>>>         struct device_attribute *attr,
>>>>>>         char *buf)
>>>>>> {
>>>>>>     struct drm_device *ddev = dev_get_drvdata(dev);
>>>>>>     struct amdgpu_device *adev = drm_to_adev(ddev);
>>>>>>     ssize_t size, offset;
>>>>>>     int ret, i;
>>>>>>     char temp_buf[512];
>>>>>>     char clock_type[] = {OD_SCLK, OD_MCLK, OD_VDDC_CURVE,
>>>>>>                          OD_VDDGFX_OFFSET, OD_RANGE, OD_CCLK};
>>>>>>
>>>>>>     if (amdgpu_in_reset(adev))
>>>>>>         return -EPERM;
>>>>>>     if (adev->in_suspend && !adev->in_runpm)
>>>>>>         return -EPERM;
>>>>>>
>>>>>>     ret = pm_runtime_get_sync(ddev->dev);
>>>>>>     if (ret < 0) {
>>>>>>         pm_runtime_put_autosuspend(ddev->dev);
>>>>>>         return ret;
>>>>>>     }
>>>>>>
>>>>>>     offset = 0;
>>>>>>
>>>>>>     if (adev->powerplay.pp_funcs->print_clock_levels) {
>>>>>>         for (i = 0; i < ARRAY_SIZE(clock_type); i++) {
>>>>>>             size = amdgpu_dpm_print_clock_levels(adev,
>>>>> clock_type[i], buf);
>>>>>>             if (offset + size > PAGE_SIZE)
>>>>>>                 break;
>>>>>>             memcpy(temp_buf + offset, buf, size);
>>>>>>             offset += size;
>>>>>>         }
>>>>>>         memcpy(buf, temp_buf, offset);
>>>>>>         size = offset;
>>>>>>     } else {
>>>>>>         size = sysfs_emit(buf, "\n");
>>>>>>     }
>>>>>>     pm_runtime_mark_last_busy(ddev->dev);
>>>>>>     pm_runtime_put_autosuspend(ddev->dev);
>>>>>>
>>>>>>     return size;
>>>>>> }
>>>>>>
>>>>> Prefer to avoid any extra stack or heap usage for buffer. Maybe 
>>>>> another arg to
>>>>> pass offset along with buf?
>>>>>
>>>> [Yu, Lang]
>>>> Actually, the buf address contains the offset(offset_in_page(buf)) .
>>>
>>> Though it's not a problem based on codeflow, static analysis tools 
>>> might complain.
>>>
>>>> Or we just rollback to sprintf/snprintf.
>>>>
>>>
>>> snprintf with (PAGE_SIZE-size) may be simpler. I think Darren took 
>>> the effort to convert these, he may have some other ideas.
>>
>> This is not what I meant. See from the design point of view the 
>> print_clock_levels() callback is the bad idea to begin with.
>>
>> What we should have instead is a callback which returns the clock as 
>> a value which is then printed in the amdgpu_get_pp_od_clk_voltage() 
>> function.
>>
>> This avoids passing around the buffer and remaining size everywhere 
>> and also guarantees that the sysfs have unified printing over all 
>> hardware generations.
>>
>
> The scenario is one node used for multiple parameters - OD_SCLK, 
> OD_CCLK, OD_VDDGFX_OFFSET etc.(mostly to avoid cluttering sysfs with 
> lots of nodes). On top of it, the parameters supported (for ex: CCLK 
> is not valid on dGPUs),  the number of levels supported etc. vary 
> across ASICs. There has to be multiple calls or the call needs to 
> return multiple values for a single parameter (for ex: up to 4, 8 or 
> 16 levels of GFXCLK depending on ASIC).

Well exactly that is questionable design for sysfs.

See the sysfs_emit() and sysfs_emit_at() functions are designed the way 
they are because you should have only one value per file, which is then 
printed at exactly one location.

Take a look at the documentation for sysfs for more details.

> I don't know the history of the callback, mostly it was considered 
> more efficient to print it directly rather than fetch and print. 
> Alex/Evan may know the details.

Yeah, somebody with a bit more background in power management needs to 
take a closer look at this here. Just keep me looped in.

Regards,
Christian.

>
> Thanks,
> Lijo
>
>> Regards,
>> Christian.
>>