[PATCH 1/2] ARM i.MX51: setup mipi

[s.hauer@pengutronix.de (Sascha Hauer)]

On Thu, Jun 07, 2012 at 03:10:05PM +0800, Shawn Guo wrote:
> On 7 June 2012 14:13, David Jander <david.jander@protonic.nl> wrote:
> > I would consider it part of SoC setup for the simple reason, that this
> > peripheral officially does not even exist (although it is physically there in
> > the chip and unfortunately _needs_ to be initialized). There is no
> > documentation of it anywhere (besides old, obsolete and unreleased manuals).
> > If one wanted to implement an IPU driver later on, there would be no way of
> > knowing that this part must be done first. We should take the chance that
> > someone happens to have this "knowledge" and do this (further harmless)
> > initialization in SoC setup, so that it is dealt with and won't get in the way
> > later. There is no worse driver developer nightmare than incomplete
> > documentation causing your otherwise correct driver to just not work.
> > OTOH, if this was an officially supported peripheral, it should have it's own
> > driver and not be part of the IPU driver either.
> >
> That does not necessarily mean imx51_soc_init() is the right place for
> that initialization, simply because not every single boot of imx51
> needs that initialization.

Since it doesn't really add to the boot time I think it won't be a
problem.

> 
> I can probably accept the mipi initialization changes if you are saying
> imx51_soc_init is not the right place for it either, but at the moment
> there is no better place than imx51_soc_init().
> 
> But why can't we do ipu reset (the second patch) in ipu driver then?

Ok, we might have to come up with something better. I originally had the
IPU reset in the IPU driver (copied from the FSL BSP). There are two
problems with this:

- The IPU reset is external to the IPU which means that we have to
  distinguish between SoCs.
- The IPU reset takes quite a long time (about 300ms). Doing this in
  the IPU driver means that the kernel boot delays for this time. Doing
  this in early init means that the 300ms can be spent bringing the rest
  of the system up.

As said, there are more clean ways to do this without having the two
mentioned problems, I'm just not sure whether it's worth it to put
significant amount of work into this.

Sascha

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