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SubjectRe: [PATCH v3 8/9] dma-buf/sync_file: Add SET_DEADLINE ioctl
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Am 27.09.21 um 10:42 schrieb Pekka Paalanen:
> On Fri, 3 Sep 2021 11:47:59 -0700
> Rob Clark <robdclark@gmail.com> wrote:
>
>> From: Rob Clark <robdclark@chromium.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.
>>
>> Signed-off-by: Rob Clark <robdclark@chromium.org>
>> ---
>> drivers/dma-buf/sync_file.c | 19 +++++++++++++++++++
>> include/uapi/linux/sync_file.h | 20 ++++++++++++++++++++
>> 2 files changed, 39 insertions(+)
>>
>> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
>> index 394e6e1e9686..f295772d5169 100644
>> --- a/drivers/dma-buf/sync_file.c
>> +++ b/drivers/dma-buf/sync_file.c
>> @@ -459,6 +459,22 @@ 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)
>> {
>> @@ -471,6 +487,9 @@ 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..f67d4ffe7566 100644
>> --- a/include/uapi/linux/sync_file.h
>> +++ b/include/uapi/linux/sync_file.h
>> @@ -67,6 +67,18 @@ 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
> Hi Rob,
>
> I think you need to specify which clock this timestamp must be in.
>
> Which epoch? Sounds a bit like CLOCK_REALTIME to me which would not
> make sense.

Most likely CLOCK_MONOTONIC I think since that's what ktime is based on
as well IIRC.

My recollection might be wrong but I think Daniel documented somewhere
that an absolut 64bit nanosecond value should be used for timeouts in
IOCTLs which is sufficient for ~500 years uptime.

So the separation between seconds and nanoseconds might be redundant.

Regards,
Christian.

>
> Also I cannot guess how a compositor should be using this, so
> explaining the expected usage would be really good, with reasons for
> why should userspace bother.
>
>
> Thanks,
> pq
>
>> + */
>> +struct sync_set_deadline {
>> + __s64 tv_sec;
>> + __s32 tv_nsec;
>> + __u32 pad;
>> +};
>> +
>> #define SYNC_IOC_MAGIC '>'
>>
>> /**
>> @@ -95,4 +107,12 @@ 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 */

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