Re: [PATCH] ARM: AM335x: Beaglebone: Fix memory setup for Beaglebone black

[Sascha Hauer <s.hauer@pengutronix.de>]

On Tue, Jun 17, 2014 at 09:35:17AM +0400, Antony Pavlov wrote:
> On Mon, 16 Jun 2014 23:35:13 +0200
> Sascha Hauer <s.hauer@pengutronix.de> wrote:
> 
> > Hi Antony,
> > 
> > On Mon, Jun 16, 2014 at 09:08:59PM +0400, Antony Pavlov wrote:
> > > On Mon, 16 Jun 2014 17:13:54 +0200
> > > Philipp Zabel <p.zabel@pengutronix.de> wrote:
> > > 
> > > Question to Sascha.
> > > 
> > > Can we preserve the 'memory' dts record in situations like this?
> > > 
> > > Is it possible just alter dts in early init code?
> > > Or something else?
> > 
> > For what do you want to preserve it? barebox never uses the memory node
> > directly to pass it to the kernel. The barebox memory banks are
> > initialized from the code and from the dts. When starting Linux the
> > memory node is (re)populated with the barebox memory banks
> > 
> > I may misunderstand what you are trying to archieve.
> 
> Imagine a family of boards. The RAM size can vary from board to board
> (for simplicity suppose that all over conditions are the same).
> Suppose I have a reliable RAM size detection routine and I want to run
> just the same barebox image on different boards.
> I want to run dts enabled Linux on all boards.

In this case don't specify the memory size in the devicetree. In a
mem_initcall detect the actual RAM size you have and call
arm_add_mem_device() accordingly. That's all. The rest will be handled
automatically. See of_memory_fixup(), this will iterate over the memory
banks and set the memory node to the correct values.

> 
> How can I handle this situation correctly?
> 
> Also note that on MIPS boards barebox uses no more than 256 MiB of RAM
> (even if a board has more than 256 MiB of RAM). It's a measure to make
> mips barebox simplier.
> I want to pass information on all available RAM to linux via dts.
> Can you describe reasonable barebox behaviour in this situation please?

Hmm, not easy. I assumed barebox knows all available memory. What
prevents you from registering all memory? I remember MIPS has a cached
mapping of the SDRAM. Is this the reason?

Sascha

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