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

From: Stephen Boyd <sboyd@kernel.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Kumar Gala" <kumar.gala@linaro.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Nicolas Pitre" <nico@fluxnic.net>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Lukasz Stelmach" <l.stelmach@samsung.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Bjorn Andersson" <bjorn.andersson@linaro.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	"Chris Brandt" <chris.brandt@renesas.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Eric Miao" <eric.miao@nvidia.com>,
	"Dmitry Osipenko" <digetx@gmail.com>,
	"Laura Abbott" <labbott@redhat.com>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>
Subject: Re: [PATCH/RFC v7] ARM: boot: Obtain start of physical memory from DTB
Date: Mon, 03 Aug 2020 12:46:53 -0700	[thread overview]
Message-ID: <159648401388.1360974.8036993510375175974@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <CAMuHMdWo2hfDfg5n1i0hHzVpEj3SG_0cMmUwuXggYETCYuOUCA@mail.gmail.com>

Quoting Geert Uytterhoeven (2020-08-03 03:18:08)
> Hi Stephen,
> 
> On Thu, Jul 23, 2020 at 3:19 AM Stephen Boyd <sboyd@kernel.org> wrote:
> > Quoting Linus Walleij (2020-07-21 05:58:59)
> > > On Mon, Jul 20, 2020 at 11:53 AM Arnd Bergmann <arnd@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.

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