linux-kernel - Re: [PATCH V1] accel/amdxdna: Add ioctl DRM_IOCTL_AMDXDNA_GET

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Message-ID: <c0c465c3-6ab6-615a-781a-e819941d33ff@amd.com>
Date: Wed, 27 Aug 2025 13:06:21 -0700
From: Lizhi Hou <lizhi.hou@....com>
To: Mario Limonciello <mario.limonciello@....com>, <ogabbay@...nel.org>,
	<quic_jhugo@...cinc.com>, <jacek.lawrynowicz@...ux.intel.com>,
	<dri-devel@...ts.freedesktop.org>
CC: <linux-kernel@...r.kernel.org>, <max.zhen@....com>, <sonal.santan@....com>
Subject: Re: [PATCH V1] accel/amdxdna: Add ioctl DRM_IOCTL_AMDXDNA_GET_ARRAY


On 8/27/25 11:09, Mario Limonciello wrote:
> On 8/27/2025 11:41 AM, Lizhi Hou wrote:
>>
>> On 8/26/25 17:31, Mario Limonciello wrote:
>>> On 8/26/2025 1:10 PM, Lizhi Hou wrote:
>>>>
>>>> On 8/26/25 10:58, Mario Limonciello wrote:
>>>>> On 8/26/2025 12:55 PM, Lizhi Hou wrote:
>>>>>>
>>>>>> On 8/26/25 10:18, Mario Limonciello wrote:
>>>>>>> On 8/25/2025 11:48 PM, Lizhi Hou wrote:
>>>>>>>>
>>>>>>>> On 8/25/25 14:28, Mario Limonciello wrote:
>>>>>>>>> On 8/22/2025 12:23 PM, Lizhi Hou wrote:
>>>>>>>>>> Add interface for applications to get information array. The 
>>>>>>>>>> application
>>>>>>>>>> provides a buffer pointer along with information type, 
>>>>>>>>>> maximum number of
>>>>>>>>>> entries and maximum size of each entry. The buffer may also 
>>>>>>>>>> contain match
>>>>>>>>>> conditions based on the information type. After the ioctl 
>>>>>>>>>> completes, the
>>>>>>>>>> actual number of entries and entry size are returned.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Lizhi Hou <lizhi.hou@....com>
>>>>>>>>>
>>>>>>>>> How does userspace discover whether or not the new IOCTL call 
>>>>>>>>> is supported?  Just a test call?
>>>>>>>> The kernel header version will be used to determine whether the 
>>>>>>>> application which uses new IOCTL will be compiled or not.
>>>>>>>>
>>>>>>>
>>>>>>> But it's not actually an application compile time decision, it's 
>>>>>>> a runtime decision.  IE I can compile an application with the 
>>>>>>> headers on kernel 6.18 that has this, but if I try to run it on 
>>>>>>> 6.15 it's going to barf.
>>>>>>>
>>>>>>> To some extent that comes with the territory, but I'm wondering 
>>>>>>> if a better solution going forward would be for there to be a 
>>>>>>> dedicated version command that you bump.
>>>>>>
>>>>>> For in-tree driver, I did not aware a common way for this other 
>>>>>> than checking the kernel version.
>>>>>>
>>>>>> And here is qaic patch of adding a new IOCTL.
>>>>>>
>>>>>> https://github.com/torvalds/linux/ 
>>>>>> commit/217b812364d360e1933d8485f063400e5dda7d66
>>>>>>
>>>>>>
>>>>>> I know there is major, minor, patchlevel in struct drm_driver. 
>>>>>> And I think that is not required for in-tree driver.
>>>>>>
>>>>>> Please let me know if I missed anything.
>>>>>>
>>>>>> Thanks,
>>>>>
>>>>> Right; so bump up one of those so that userspace can check it. 
>>>>> Maybe "minor"?
>>>>
>>>> I meant for in-tree driver, is it good enough for userspace to just 
>>>> check kernel version?  E.g. The drm driver versions are not used by 
>>>> ivpu or qaic.
>>>>
>>>
>>> Just because they don't doesn't mean you shouldn't.
>> Ok. :) It does not sound amdxdna specific. Just wondering how the 
>> other driver/application under accel subsystem handle this.
>>>
>>> Take a look at what amdgpu does for user queues earlier this year 
>>> for example: 100b6010d7540e
>>>
>>> This means that a userspace application can look for that minor bump 
>>> or newer to know the ioctl supports user queues.
>>
>> As in-tree driver is part of kernel, the userspace application can 
>> check kernel version to determine whether a feature is supported or 
>> not. Could you share the idea why would user application to check drm 
>> driver version for this?
>>
>> And amdxdna driver is new added driver which never bumped drm major/ 
>> minor before. Thus there is not any application use drm versions. 
>> Maybe using kernel version directly is good enough in this case?
>>
>> I am fine to bump minor if it provides better support to user 
>> applications.
>>
>>
>> Thanks,
>>
>> Lizhi
>>
>
> If you're running mainline kernel I totally agree with you that you 
> can make a runtime call based upon major/minor kernel version.  To me 
> the problem ends up being cases that distros do a backport of a driver 
> or subsystem that this falls apart.
>
> For example RHEL and CentOS stream both do this, and then such 
> comparisons can no longer be made accurately.

Ok. I will bump minor by 1.

Lizhi