Re: [RFC/PATCH 0/1] New subdev sensor operation g_interface_parms

[Hans Verkuil <hansverk@cisco.com>]

On Wednesday, February 23, 2011 16:30:42 Laurent Pinchart wrote:
> On Wednesday 23 February 2011 15:06:49 Aguirre, Sergio wrote:
> > <snip>
> > 
> > > > The only static data I am concerned about are those that affect signal
> > > > integrity.
> > > 
> > > > After thinking carefully about this I realized that there is really
> > > > only one setting that is relevant to that: the sampling edge. The
> > > > polarities do not matter in this.
> > 
> > I respectfully disagree.
> 
> So do I. Sampling edge is related to polarities, so you need to take both 
into 
> account.

When you switch polarity for data/field/hsync/vsync signals on a simple bus 
you just invert whether a 1 bit is output as high or low voltage. So you just 
change the meaning of the bit. This does not matter for signal integrity, 
since you obviously have to be able to sample both low and high voltages. It 
is *when* you sample that can have a major effect.

This might be different for differential clocks. I have no experience with 
this, so I can't say anything sensible about that.

Regards,

	Hans

> 
> > AFAIK, There is not such thing as sampling edge configuration for MIPI
> > Receivers, and the polarities DO matter, since it's a differential
> > signal.
> > 
> > > Ok, this is much better! I'm still not perfectly happy having to punish
> > > all just for the sake of a couple of broken boards, but I can certainly
> > > much better live with this, than with having to hard-code each and every
> > > bit. Thanks, Hans!
> > > 
> > > So, I think, we can proceed with this, let's see the code now, shall
> > > we?;)
> > > 
> > > Currently soc-camera auto-configures the following parameters:
> > > 
> > > hsync polarity
> > > vsync polarity
> > > data polarity
> > > master / slave mode
> 
> What do you mean by master/slave mode ?
> 
> > > data bus width
> 
> The data bus width can already be configured through the media bus format. 
Do 
> we need to set it explicitly ?
> 
> > > pixel clock polarity
> > >
> > > (see include/media/soc_camera.h::soc_camera_bus_param_compatible() and
> > > drivers/media/video/soc_camera.c::soc_camera_apply_sensor_flags()).
> > > Removing the pixclk polarity, the rest we can use as a basis for a new
> > > subdev-based implementation.
> > 
> > Don't we need to move this out from soc_camera and make it available in
> > v4l2_subdev ops? (I'm talking about both parallel and the "new" MIPI
> > support)
> > 
> > That way both SoC_Camera, and Media Controller frameworks can use that.
> 
> -- 
> Regards,
> 
> Laurent Pinchart
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