Re: [RFC PATCH v3 0/3] Querying errors from drm_syncobj

[Michel Dänzer]

On 2/25/26 14:25, Christian König wrote:
> On 2/25/26 13:46, Yicong Hui wrote:
>> This patch series adds 2 new flags, DRM_SYNCOBJ_QUERY_FLAGS_ERROR and
>> DRM_SYNCOBJ_WAIT_FLAGS_ABORT_ON_ERROR for 3 ioctl operations
>> DRM_IOCTL_SYNCOBJ_QUERY, DRM_IOCTL_SYNCOBJ_WAIT and
>> DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT to allow them to batch-request error
>> codes from multiple syncobjs and abort early upon error of any of them.
> 
> Patch #1 looks good enough to add my rb.
> 
> Patch #2 looks good as well, but I'm not familiar enough with the code and have no time to wrap my head around it to give a review.
> 
> Adding a few people on CC, maybe somebody has time to take another look.
> 
>>
>> Based on discussions from Michel Dänzer and Christian König, and a
>> starter task from the DRM todo documentation.
>>
>> See https://gitlab.gnome.org/GNOME/mutter/-/issues/4624 for discussions
>> on userspace implementation.
>>
>> I have looked into adding sub test cases into syncobj_wait.c and
>> syncobj_timeline.c, igt-tests for this and I think I understand the 
>> process for writing tests and submitting them, however, these ioctls 
>> only trigger in the case that there is an error, but I am not sure what
>> is the best way to artifically trigger an error from userspace in order
>> to test that these ioctl flags work. What's the recommended way to 
>> approach this?
> 
> When Michel agrees that this is the way to go then we either need an in-kernel selftest (see directory drivers/gpu/drm/tests/) or an userspace IGT test.
> 
> Not sure what is more appropriate, maybe somebody on CC has more experience with that.

I'd advise against landing this in the kernel before there's a corresponding display server implementation making use of it, in a mergeable state.

Otherwise you might end up with the kernel having to support UAPI which no real-world user space actually uses. Been there, done that myself.


I don't have the capacity to contribute anything more than advice at this point.


-- 
Earthling Michel Dänzer       \        GNOME / Xwayland / Mesa developer
https://redhat.com             \               Libre software enthusiast