[PATCH/RFC v7] ARM: boot: Obtain start of physical memory from DTB

[Stephen Boyd]

Quoting Geert Uytterhoeven (2020-08-03 03:18:08)
> Hi Stephen,
> 
> On Thu, Jul 23, 2020 at 3:19 AM Stephen Boyd <sboyd at kernel.org> wrote:
> > Quoting Linus Walleij (2020-07-21 05:58:59)
> > > On Mon, Jul 20, 2020 at 11:53 AM Arnd Bergmann <arnd at arndb.de> wrote:
> > > > No idea what /exactly/ is going wrong, but I would point out that this is one
> > > > of the platforms that is handled as a special case in the Makefile when
> > > > setting TEXT_OFFSET:
> > > (...)
> > > > textofs-$(CONFIG_ARCH_IPQ40XX) := 0x00208000
> > > > textofs-$(CONFIG_ARCH_MSM8X60) := 0x00208000
> > > > textofs-$(CONFIG_ARCH_MSM8960) := 0x00208000
> > >
> > > But what on earth is this? I just deleted this and the platform
> > > boots just as well.
> >
> > We need to shift the kernel text to start 2MB beyond the start of memory
> > because there is the shared memory region used to communicate with other
> > processors in the SoC there. It took a while for us to convince other OS
> > folks in the company to put shared memory somewhere else besides the
> > start of RAM, but eventually we won that battle.
> >
> > Does your booted kernel have its text section at the start of RAM or is
> > it offset by 2MB without this change? Check out /proc/iomem to see where
> > the kernel text is in relation to the start of RAM. I think the problem
> > is the decompressor would have to parse the reserved memory sections in
> > DT to figure out that it shouldn't decompress over shared memory, and
> > changing the decompressor to do that was deemed "hard". Does this patch
> > series resolve that?
> 
> As this patch adds C code to extract the start of memory from DT, it
> should be quite easy to add code to filter out regions marked reserved
> in DT.  In fact that would be a prerequisite for making this work with
> crashkernel support (+ making the crashkernel code mark its memory as
> reserved in DT).
> 

Cool. Sounds like that may need to be done then before it works on these
particular qcom platforms.