Re: [PATCH v6 9/9] ARM: vexpress: Add Device Tree for V2P-CA15 core tile (TC1 variant)

[Dave Martin <dave.martin-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Mon, Jan 30, 2012 at 02:31:15PM -0700, Grant Likely wrote:
> On Mon, Jan 30, 2012 at 05:42:12PM +0000, Dave Martin wrote:
> > On Wed, Jan 25, 2012 at 05:43:16PM +0000, Pawel Moll wrote:
> > > On Thu, 2012-01-19 at 17:00 +0000, David Vrabel wrote:
> > > > > Ok, /include/ "skeleton.dtsi" is gone then :-)
> > > > 
> > > > The problem wasn't with including skeleton.dtsi.  With
> > > > CONFIG_ARM_ATAG_DTB_COMPAT the zImage decompressor modifies the appended
> > > > DTB using information from the ATAGs (see atags_to_fdt()).
> > > > 
> > > > If there's an ATAG giving the amount of RAM the DTB's "memory" node is
> > > > replaced with a new one.  Since the vexpress DTBs don't have a "memory"
> > > > node it's added and the DTB ends up with two nodes describing memory.
> > > 
> > > As it turned out it was just the "skeleton.dtsi" problem after all - I
> > > mean the fact that there where two device_type="memory" nodes in the
> > > tree.
> > > 
> > > The decompressor's setprop()
> > > (arch/arm/boot/compressed/atags_to_fdt.c:12) uses libfdt's
> > > fdt_setprop(), which correctly ignores the "@00000000" component of the
> > > node name and sets the reg property as expected. So as long as there is
> > > exactly one "memory[@address]" node in the tree,
> > > CONFIG_ARM_ATAG_DTB_COMPAT is happy.
> > > 
> > > I will remove the /include/ from the dts files for VE (see below) in the
> > > v3.3-rc1 based series.
> > > 
> > > Thanks for spotting this!
> > > 
> > > Pawe??
> > 
> > This carries a significant risk of unintended fragmentation and buggy
> > maintenance.  This patch is a good example of the kind of change which
> > could easily go wrong.  (I'm not saying that it is wrong -- just using
> > it as an example.)
> > 
> > Since we will end up with a significantly large number of device trees
> > for vexpress, I can foresee that we'll end up with a highly reduncant
> > set of .dts{,i} files (each of which is often rather internally redundant
> > too).
> > 
> > Does anyone have a view on whether it's acceptable to generate device
> > tree sources from another form, instead of having them verbatim in the
> > kernel tree?  This could involve a preprocessor, or something more
> > heavyweight.
> 
> Yes, the xilinx folks have been using a dts generator to create the
> device tree that matches an FPGA design.  This works on ppc and
> microblaze, and they'll do the same thing for their ARM FPGA SoC.

OK, well I guess it's good to know we have the option to consider such
techniques for vexpress in the future.

For now, I suggest we paste in the .dts files as-is, since the situation
is not too unmanageable for now, and we don't unnecessary feature creep
to hold up merging of the series.

Cheers
---Dave