Re: [PATCH v3 09/33] v4l: Add subdev selections documentation

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Hi Laurent,

On Fri, Mar 02, 2012 at 06:54:48PM +0100, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Friday 02 March 2012 14:24:40 Sakari Ailus wrote:
> > On Tue, Feb 28, 2012 at 12:42:26PM +0100, Laurent Pinchart wrote:
> > > On Sunday 26 February 2012 23:42:19 Sakari Ailus wrote:
> > > > Laurent Pinchart wrote:
> > > > > On Monday 20 February 2012 03:56:48 Sakari Ailus wrote:
> 
> > > > >> +      </section>
> > > > >> 
> > > > >> -      <para>Cropping behaviour on output pads is not defined.</para>
> > > > >> +    </section>
> > > > >> +
> > > > >> +    <section>
> > > > >> +      <title>Order of configuration and format propagation</title>
> > > > >> +
> > > > >> +      <para>Inside subdevs, the order of image processing steps will
> > > > >> +      always be from the sink pad towards the source pad. This is
> > > > >> also
> > > > >> +      reflected in the order in which the configuration must be
> > > > >> +      performed by the user: the changes made will be propagated to
> > > > >> +      any subsequent stages. If this behaviour is not desired, the
> > > > >> +      user must set
> > > > >> +      <constant>V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG</constant> flag.
> > > > > 
> > > > > Could you explain what happens when V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG
> > > > > is
> > > > > set ? Just stating that it doesn't follow the propagation behaviour
> > > > > previously described could be understood in many different ways.
> > > > 
> > > > Good point. How about this:
> > > > 
> > > > "This flag causes that no propagation of the changes are allowed in any
> > > > circumstances. This may also lead the accessed rectangle not being
> > > > changed at all,
> > > 
> > > "The accessed rectangle will likely be adjusted by the driver,"
> > 
> > Why "likely"? I think it should say "may" instead, but this of course
> > depends on what the user asks.
> 
> I'm fine with "The accessed rectangle may be adjusted by the driver" (or 
> s/may/can/, as adjusting the rectangle is part of the negotiation mechanism 
> and is thus more likely than not).
> 
> > > > depending on the properties of the underlying hardware.
> > > > Some drivers may not support this flag."
> > > 
> > > What should happen then ? Should the flag be ignored, or should the driver
> > > return an error ?
> > 
> > Only the SMIA++ driver supports this flag so far (as goes for the subdev
> > selection interface).
> > 
> > I think it should be ignored. Consider a situation that we add a new flag
> > which most of the drivers are unaware of.
> > 
> > As we're adding the flag right at the time the interface is introduced, we
> > could also require that all drivers must support it. How about that? In that
> > case I'd remove the last sentence of that paragraph.
> 
> I think I'd like that better. Otherwise applications would be forced to check 
> the returned rectangle to find out if the flag was taken into account.

Fixed for the next one.

Cheers,

-- 
Sakari Ailus
e-mail: sakari.ailus@xxxxxx	jabber/XMPP/Gmail: sailus@xxxxxxxxxxxxxx
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