Re: [PATCH 05/11] [POWERPC] TQM5200 DTS

["Grant Likely" <grant.likely@secretlab.ca>]

On 10/29/07, Marian Balakowicz <m8@semihalf.com> wrote:
> David Gibson wrote:
> > On Thu, Oct 25, 2007 at 05:46:19PM +0200, Marian Balakowicz wrote:
> >> Grant Likely wrote:
> >>> On 10/25/07, Martin Krause <Martin.Krause@tqs.de> wrote:
> > [snip]
> >>>> On a board with 16 MiB FLASH for example the "big-fs" _and_ the "misc"
> >>>> partition could not be used. "big-fs", because the memory is too small
> >>>> (which is OK) and "misc", because it overlaps 1 MiB over the physikal
> >>>> flash border. So only the first 9 MiB of the flash could be used in Linux.
> >>>> The remaining 7 MiB couldn't be accessed.
> >>> Perhaps it would be better to drop the flash layout from the in-kernel
> >>> dts files entirely since flash layout can be a fluid thing.
> >> Well, but that would not be really user friendly, I'd rather stick
> >> with some default config.
> >
> > Strictly speaking the device-tree is not the right place for flash
> > partitioning information.  We put it there because it's preferable to
> > having hardcoded per-board flash layouts in the code itself.
> >
> > It only really works well, though, when there are strong conventions
> > (shared with the firmware) about how to partition the flash.
> >
> > Where it's really up to the user to determine how they want to lay out
> > their flash, putting things in the device tree isn't a really good
> > idea.
>
> In principle, you are right, we should not be putting a user dependent
> configuration into .dts files. But on the other hand, bindings have
> been defined for flash-like devices and their partition layouts and
> physmap_of device driver is expecting to get this information from the
> blob. So, it is the place for it. But if we are not to put partition
> layouts into the default kernel .dts files then we should
> provide/maintain some examples an that may be a even bigger mess.
>
> > Incidentally, it's not required that *all* the flash address space be
> > in partitions, so it is possible only give partitions for those flash
> > chunks which the firmware needs to know about.
>
> That might be nicer solution but different variants of TQM5200 boards
> do not share the same subset of partitions (default u-boot partitions
> at least), so it will not help much.

It's probably more appropriate to have the flash partition layout in
the u-boot environment and have u-boot populate the partition
information in the device tree.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
grant.likely@secretlab.ca
(403) 399-0195