PRAM and reserved memory for Linux

[Tom Rini]

On Wed, Jul 13, 2022 at 04:13:27PM +0000, Joakim Tjernlund wrote:
> On Wed, 2022-07-13 at 10:21 -0400, Tom Rini wrote:
> > On Wed, Jul 13, 2022 at 10:08:38AM +0000, Joakim Tjernlund wrote:
> > 
> > > I added CONFIG_PRAM 4 and a reserved-memory DTS node for the same space but
> > > now u-boot complains when booting:
> > >   ERROR: reserving fdt memory region failed (addr=703ff000 size=1000)
> > > The error is caused by arch_lmb_reserve() in arm which seem
> > > to reserve command line and board info ? 
> > > 
> > > If I remove the reserved-memory DTS node I don't get a reserved area in Linux,
> > > don't quite understand how PRAM is supposed to work?
> > 
> > The first likely problem is that CONFIG_PRAM stuff isn't often used
> > these days so might be glitchy / buggy, as you've found here.  Next, I
> > bet that area in arch_lmb_reserve() is about ATAGS/related and should be
> > guarded with CONFIG_SUPPORT_PASSING_ATAGS.
> > 
> 
> The  arch_lmb_reserve() comment reads(lots of archs has similar code):
> 	/*
> 	 * Booting a (Linux) kernel image
> 	 *
> 	 * Allocate space for command line and board info - the
> 	 * address should be as high as possible within the reach of
> 	 * the kernel (see CONFIG_SYS_BOOTMAPSZ settings), but in unused
> 	 * memory, which means far enough below the current stack
> 	 * pointer.
> 
> You still think this cmdline/board info is just for the old ATAGS ?
> I have an older boot and it des not have CONFIG_SUPPORT_PASSING_ATAGS but
> CMDLINE_TAG etc. is here though.

Yes it is, and SUPPORT_PASSING_ATAGS is somewhat new in that I added it
when converting CMDLINE_TAG, etc, to Kconfig and making it be easier to
say "this platform is new enough to never ever need this".

-- 
Tom
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