Re: [GIT PULL FOR v3.10] Camera sensors patches

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Mauro,

On Monday 15 April 2013 09:42:48 Mauro Carvalho Chehab wrote:
> Em Mon, 15 Apr 2013 12:19:23 +0200 Laurent Pinchart escreveu:
> > On Sunday 14 April 2013 16:59:58 Mauro Carvalho Chehab wrote:
> > > Em Fri, 12 Apr 2013 11:13:06 +0200 Laurent Pinchart escreveu:
> > > > Hi Mauro,
> > > > 
> > > > The following changes since commit
> > 
> > 81e096c8ac6a064854c2157e0bf802dc4906678c:
> > > >   [media] budget: Add support for Philips Semi Sylt PCI ref. design
> > > > 
> > > > (2013-04-08 07:28:01 -0300)
> > > > 
> > > > are available in the git repository at:
> > > >   git://linuxtv.org/pinchartl/media.git sensors/next
> > > > 
> > > > for you to fetch changes up to 
c890926a06339944790c5c265e21e8547aa55e49:
> > > >   mt9p031: Use the common clock framework (2013-04-12 11:07:07 +0200)
> > > > 
> > > > ----------------------------------------------------------------
> > > > 
> > > > Laurent Pinchart (5):
> > > >       mt9m032: Fix PLL setup
> > > >       mt9m032: Define MT9M032_READ_MODE1 bits
> > > >       mt9p031: Use devm_* managed helpers
> > > >       mt9p031: Add support for regulators
> > > >       mt9p031: Use the common clock framework
> > > 
> > > Hmm... It seems ugly to have regulators and clock framework and other
> > > SoC calls inside an i2c driver that can be used by a device that doesn't
> > > have regulators.
> > > 
> > > I'm not sure what's the best solution for it, so, I'll be adding those
> > > two patches, but it seems that we'll need to restrict the usage of those
> > > calls only if the caller driver is a platform driver.
> > 
> > The MT9P031 needs power supplies and a clock on all platforms, regardless
> > of the bridge bus type.
> 
> Well, all digital devices require clock and power. If power is either a
> simple electric circuit, a battery or a regulator, that depends on the
> board.
>
> > I suppose the use case that mostly concerns you here is
> > USB webcams
> 
> Yes.
> 
> > where the power supplies and the clock are controlled automatically by the
> > device.
> 
> Or could be not controlled at all. It could be a simple XTAL attached to the
> sensor or a clock signal provided by the bridge obtained from a fixed XTAL,
> and a resistor bridge or a Zenner diode providing the needed power voltage.
>
> > If we ever need to support such a device in the future we can of course
> > revisit the driver then, and one possible solution would be to register
> > fixed voltage regulators and a fixed clock.
> 
> That is an overkill: devices were the power supply/xtal clock can't be
> controlled should not require extra software that pretend to control it.

If I'm not mistaken that's however the recommended way on embedded devices at 
the moment. I don't have a strong opinion on the subject for now, but this 
will need to be at least discussed with core clock and regulator developers.

-- 
Regards,

Laurent Pinchart