linux-kernel - Re: [PATCH v4 05/14] dma-buf/sync_file: Add SET

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Date:   Thu, 23 Feb 2023 10:19:40 +0100
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Rob Clark <robdclark@...il.com>,
        Christian König <christian.koenig@....com>
Cc:     dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Daniel Vetter <daniel@...ll.ch>,
        Michel Dänzer <michel@...nzer.net>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Simon Ser <contact@...rsion.fr>,
        Rob Clark <robdclark@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        "open list:SYNC FILE FRAMEWORK" <linux-media@...r.kernel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 05/14] dma-buf/sync_file: Add SET_DEADLINE ioctl

Am 20.02.23 um 17:09 schrieb Rob Clark:
> On Mon, Feb 20, 2023 at 12:27 AM Christian König
> <christian.koenig@....com> wrote:
>> Am 18.02.23 um 22:15 schrieb Rob Clark:
>>> From: Rob Clark <robdclark@...omium.org>
>>>
>>> The initial purpose is for igt tests, but this would also be useful for
>>> compositors that wait until close to vblank deadline to make decisions
>>> about which frame to show.
>>>
>>> The igt tests can be found at:
>>>
>>> https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadline
>>>
>>> v2: Clarify the timebase, add link to igt tests
>>>
>>> Signed-off-by: Rob Clark <robdclark@...omium.org>
>>> ---
>>>    drivers/dma-buf/sync_file.c    | 19 +++++++++++++++++++
>>>    include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++
>>>    2 files changed, 41 insertions(+)
>>>
>>> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
>>> index af57799c86ce..fb6ca1032885 100644
>>> --- a/drivers/dma-buf/sync_file.c
>>> +++ b/drivers/dma-buf/sync_file.c
>>> @@ -350,6 +350,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>>>        return ret;
>>>    }
>>>
>>> +static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
>>> +                                     unsigned long arg)
>>> +{
>>> +     struct sync_set_deadline ts;
>>> +
>>> +     if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))
>>> +             return -EFAULT;
>>> +
>>> +     if (ts.pad)
>>> +             return -EINVAL;
>>> +
>>> +     dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec));
>>> +
>>> +     return 0;
>>> +}
>>> +
>>>    static long sync_file_ioctl(struct file *file, unsigned int cmd,
>>>                            unsigned long arg)
>>>    {
>>> @@ -362,6 +378,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd,
>>>        case SYNC_IOC_FILE_INFO:
>>>                return sync_file_ioctl_fence_info(sync_file, arg);
>>>
>>> +     case SYNC_IOC_SET_DEADLINE:
>>> +             return sync_file_ioctl_set_deadline(sync_file, arg);
>>> +
>>>        default:
>>>                return -ENOTTY;
>>>        }
>>> diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h
>>> index ee2dcfb3d660..c8666580816f 100644
>>> --- a/include/uapi/linux/sync_file.h
>>> +++ b/include/uapi/linux/sync_file.h
>>> @@ -67,6 +67,20 @@ struct sync_file_info {
>>>        __u64   sync_fence_info;
>>>    };
>>>
>>> +/**
>>> + * struct sync_set_deadline - set a deadline on a fence
>>> + * @tv_sec:  seconds elapsed since epoch
>>> + * @tv_nsec: nanoseconds elapsed since the time given by the tv_sec
>>> + * @pad:     must be zero
>>> + *
>>> + * The timebase for the deadline is CLOCK_MONOTONIC (same as vblank)
>>> + */
>>> +struct sync_set_deadline {
>>> +     __s64   tv_sec;
>>> +     __s32   tv_nsec;
>>> +     __u32   pad;
>> IIRC struct timespec defined this as time_t/long (which is horrible for
>> an UAPI because of the sizeof(long) dependency), one possible
>> alternative is to use 64bit nanoseconds from CLOCK_MONOTONIC (which is
>> essentially ktime).
>>
>> Not 100% sure if there is any preferences documented, but I think the
>> later might be better.
> The original thought is that this maps directly to clock_gettime()
> without extra conversion needed, and is similar to other pre-ktime_t
> UAPI.  But OTOH if userspace wants to add an offset, it is maybe
> better to convert completely to ns in userspace and use a u64 (as that
> is what ns_to_ktime() uses).. (and OFC whatever decision here also
> applies to the syncobj wait ioctls)
>
> I'm leaning towards u64 CLOCK_MONOTONIC ns if no one has a good
> argument against that.

+1 for that.

Regards,
Christian.

>
> BR,
> -R
>
>> Either way the patch is Acked-by: Christian König
>> <christian.koenig@....com> for this patch.
>>
>> Regards,
>> Christian.
>>
>>> +};
>>> +
>>>    #define SYNC_IOC_MAGIC              '>'
>>>
>>>    /**
>>> @@ -95,4 +109,12 @@ struct sync_file_info {
>>>     */
>>>    #define SYNC_IOC_FILE_INFO  _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
>>>
>>> +
>>> +/**
>>> + * DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence
>>> + *
>>> + * Allows userspace to set a deadline on a fence, see dma_fence_set_deadline()
>>> + */
>>> +#define SYNC_IOC_SET_DEADLINE        _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
>>> +
>>>    #endif /* _UAPI_LINUX_SYNC_H */