Re: [PATCH/RFC] ARM: boot: Relax kernel image alignment for RZ/A with CS3 SDRAM - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
	"Nicolas Pitre" <nico@fluxnic.net>,
	"Eric Miao" <eric.miao@nvidia.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Chris Brandt" <chris.brandt@renesas.com>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH/RFC] ARM: boot: Relax kernel image alignment for RZ/A with CS3 SDRAM
Date: Wed, 13 Nov 2019 17:04:25 +0000	[thread overview]
Message-ID: <20191113170425.GQ25745@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAMuHMdXWsUChMA+_6sdavo8nd-9icX6nsN7unSfMMViOQrUVMQ@mail.gmail.com>

On Wed, Nov 13, 2019 at 02:32:19PM +0100, Geert Uytterhoeven wrote:
> Hi Russell,
> 
> On Wed, Nov 13, 2019 at 11:39 AM Russell King - ARM Linux admin
> <linux@armlinux.org.uk> wrote:
> > On Wed, Nov 13, 2019 at 11:27:29AM +0100, Geert Uytterhoeven wrote:
> > > The RZA2MEVB sub board has 64 MiB of SDRAM at 0x0C000000 (CS3 space).
> > > Hence the mask for CONFIG_AUTO_ZRELADDR needs to be changed, otherwise
> > > the system will crash because it will try to decompress a zImage or
> > > uImage to a non-RAM garbage address.
> > >
> > > Based on a patch in the BSP by Chris Brandt <chris.brandt@renesas.com>.
> > >
> > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > > ---
> > > No idea what to do with the rest of the comment, or if this breaks
> > > existing platforms.
> >
> > We occasionally have discussions about this - the last one was a big
> > one in Edinburgh, and the answer is we can't change this in mainline.
> > They've also come up on the mailing lists as well.
> >
> > I'm not going to rehash this old argument yet again - the comment
> > details the reason for it, and is there to prevent exactly this.
> 
> Sorry, I wasn't aware of that discussion.
> I had a chat about this at ELC-E with Arnd, and he was open to this change.
> 
> > If someone is silly enough to come up with a platform that violates
> > the documented 32-bit ARM booting protocol, then they can't expect
> > the kernel to bend to their platform's requirements at the expense of
> > already merged platforms.
> 
> Documentation/arm/booting.rst:
>   1. The kernel should be placed in the first 128MiB of RAM: check.
>   2. A safe location is just above the 128MiB boundary from start of RAM:
>      oops. Not all platforms have more than 128 MiB of RAM...
> 
> An alternative is to fall to the builtin 4 MiB of SRAM, or the 8 MiB of
> HyperRAM on RZA2MEVB, but doing that requires using XIP.
> Which brings us to your response in the other email:
> 
> > Are we going back to non-multi-platform kernels? ;)
> 
> Good question! ;-)
> 
>   1. CONFIG_AUTO_ZRELADDR=n
>   2. CONFIG_XIP_KERNEL=y

If you're using an XIP kernel, you are by definition not using the
decompressor.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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