Re: [PATCH] MTD Maps driver for Sharp LH7a40x

["Thomas Gleixner" <tglx@linutronix.de>]

On Saturday 19 June 2004 11:23, Russell King - ARM Linux wrote:
>
> ATAG is only ARM because Linux doesn't like binary interfaces - and
> that's one of the reasons I don't want to see it expanding more and
> more.  See the "IDE support for lh7a40x" on the linux-arm-kernel list
> for a discussion on this topic.

Ok, sounds reasonable. I did not follow this thread, as the topic was out of 
my primary interest.

> > For chips which need Vpp setting for programming and erasing this is
> > rather impossible. Same applies to NAND drivers, as the NAND interface
> > can hardly be specified board independent on the commandline.
>
> You may want to take a look at how integrator-flash.c handles this
> aspect.  The handling of VPP and write enables is platform specific
> and requires some code to do it, so obviously we can't encode that
> into an ATAG or command line argument.
>
> Note how integrator-flash.c is used on the Integrator/AP, Integrator/CP
> and Versatile/PB platforms, and notice the way the platform support code
> is separate in arch/arm/mach-integrator/integrator_*.c and
> arch/arm/mach-versatile/core.c.  I think this is a good model for
> what you're trying to achieve.

Yep. I was not aware of this. But it would have been my first choice too to 
put this into the board support files / directories which are available / 
neccecary for embedded systems anyway.

> Also note that the size of the flash doesn't have to exactly match the
> size of flash fitted to the device - it just has to be of sufficient
> size to cover the largest flash which may be fitted to your device.
> (or, if you have a way to discover the fitted flash size without too
> much hastle, then you could use that.)

I know. For NAND we use the chip ID to do that anyway.

> Eww, no thanks.  We've recently killed that in the PXA tree.  hardware.h
> is included by 99% of the kernel include files which means any modification
> to it or included files causes the whole kernel to rebuild - which takes
> long enough on x86 with gcc 3 already.
> The timer init is a mess and Deepak's been cleaning that up, so please
> don't use the current structure as a justification.
> I think you're better off using integrator-flash.c as is, and just
> supplying the relevent platform device structure and associated code.

I just said that ist possible, but weird. You're definitly right to make this 
go away.

So a final conclusion would be:

1. Add commandline parsing for flashbase,size,buswidth which covers the case 
where no special code is neccecary to access the chips.

2. Use the already existing platform model, which can be retrieved from your 
work in arch/arm/mach-xxxx

3. Extend the generic NAND driver to provide a simple mechanism to make 2.) 
work for NAND too

4. Obsolete the board specific mapping drivers in drivers/mtd/maps and 
drivers/mtd/nand when this is done.

Did I miss(understand) anything ?

-- 
Thomas
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