[PATCH v2] spi: orion.c: Add direct access mode

[arnd@arndb.de (Arnd Bergmann)]

On Tuesday 29 March 2016 12:52:30 Mark Brown wrote:
> On Tue, Mar 29, 2016 at 09:49:09PM +0200, Arnd Bergmann wrote:
> > On Tuesday 29 March 2016 09:47:58 Mark Brown wrote:
> 
> > > Well, in the cases where we have one device on the bus then it's not a
> > > big deal since we can check what the last thing we set was.  The direct
> > > access stuff is going to have trouble if we have multiple devices on the
> > > bus since we try to mix it with non-MMIO access we run the risk of
> > > conflicting simultaneous use unless we continue to route everything
> > > through the SPI subsystem (like we do with the current flash read
> > > support).
> 
> > Maybe we can avoid that if we enforce at the driver level that we
> > use the same mode for all slaves? The way I read the manual, I think
> > that's how it is intended at least.
> 
> Well, we currently don't have any XIP or whatever support at all, it's
> still only in the SPI operations so it's academic - that'd be a future
> issue if we did start doing things that accessed the memory map outside
> of the SPI flow.

Isn't this just about implementing .point()/.unpoint() in the spi-nor
driver?

> > Also, as mentioned we don't have any machine with more than one SPI
> > slave so far, so we don't really need to overengineer it and can
> > go for the simplest implementation in the SPI master driver.
> 
> For me the simplest thing seems like just using one window for all the
> devices, it seems more likely to deliver useful results without the
> system integrator having to think about how to configure this for
> optimisation.

Do you mean single-window mode? I don't see the difference to the other
modes, but that's certainly fine with me if it helps.

	Arnd