On Fri November 16 2012 16:20:03 Sakari Ailus wrote:
> Hi Hans,
>
> Thanks for the comments!
>
> On Fri, Nov 16, 2012 at 02:51:29PM +0100, Hans Verkuil wrote:
> > On Thu November 15 2012 23:06:44 Sakari Ailus wrote:
> > > diff --git a/Documentation/DocBook/media/v4l/io.xml
> > > b/Documentation/DocBook/media/v4l/io.xml
> > > index 7e2f3d7..d598f2c 100644
> > > --- a/Documentation/DocBook/media/v4l/io.xml
> > > +++ b/Documentation/DocBook/media/v4l/io.xml
> > > @@ -938,6 +938,31 @@ Typically applications shall use this flag for
> > > output buffers if the data
> > > in this buffer has not been created by the CPU but by some DMA-capable
> > > unit,
> > > in which case caches have not been used.</entry>
> > > </row>
> > > + <row>
> > > + <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_MASK</constant></entry>
> > > + <entry>0xe000</entry>
> > > + <entry>Mask for timestamp types below. To test the
> > > + timestamp type, mask out bits not belonging to timestamp
> > > + type by performing a logical and operation with buffer
> > > + flags and timestamp mask.</tt> </entry>
> > > + </row>
> > > + <row>
> > > + <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN</constant></entry>
> > > + <entry>0x0000</entry>
> > > + <entry>Unknown timestamp type. This type is used by
> > > + drivers before Linux 3.8 and may be either monotonic (see
> > > + below) or realtime. Monotonic clock has been favoured in
> > > + embedded systems whereas most of the drivers use the
> > > + realtime clock.</entry>
> >
> > Isn't 'wallclock time' a better expression? It is probably a good idea as
> > well to add the userspace call that gives the same clock: gettimeofday or
> > clock_gettime(CLOCK_REALTIME) for the wallclock time and
> > clock_gettime(CLOCK_MONOTONIC) for the monotonic time. That way apps can
> > do the same call and compare it to the timestamp received.
>
> I'll add a reference to clock_gettime() and change realtime to wall clock
> time. I wonder if I should also add that the unknown timestamp means either
> of the two, or can we allow different kinds of unknown timestamps in the
> future.
No. UNKNOWN should never be used in the future. It is specific to the pre
timestamp flag era where the timestamp is really only one of two options.
Regards,
Hans
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