Re: [PATCH] Revert "arm: bootm: Disable LMB reservation for command line and board info on arm64"

From: Tom Rini <trini@konsulko.com>
To: Marek Vasut <marex@denx.de>
Cc: Jan Kiszka <jan.kiszka@siemens.com>,
	U-Boot Mailing List <u-boot@lists.denx.de>,
	Hai Pham <hai.pham.ud@renesas.com>,
	Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>,
	Stephen Warren <swarren@nvidia.com>,
	Lokesh Vutla <lokeshvutla@ti.com>
Subject: Re: [PATCH] Revert "arm: bootm: Disable LMB reservation for command line and board info on arm64"
Date: Thu, 5 Aug 2021 19:31:03 -0400	[thread overview]
Message-ID: <20210805233103.GS858@bill-the-cat> (raw)
In-Reply-To: <4046119c-c61c-ed49-92e6-dee5f8c67b3c@denx.de>

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On Thu, Aug 05, 2021 at 11:53:24PM +0200, Marek Vasut wrote:
> On 8/2/21 3:00 PM, Tom Rini wrote:
> > On Mon, Aug 02, 2021 at 02:54:22AM +0200, Marek Vasut wrote:
> > > On 7/29/21 6:58 PM, Tom Rini wrote:
> > > 
> > > [...]
> > > 
> > > > > > so when did rcar3 introduce something there that shouldn't be
> > > > > > reserved?  And you had phrased this to me on IRC as about reserving spot
> > > > > > for ATAGS, and that not being needed of course on arm64.  But that's not
> > > > > > what's going on.  Perhaps the answer is that rcar3 needs to introduce a
> > > > > > board_lmb_reserve to free the normal arch one and provide whatever more
> > > > > > narrow scope it needs.
> > > > > 
> > > > > Based on the commit message 2359fa7a878 ("arm: bootm: Disable LMB
> > > > > reservation for command line and board info on arm64") , this is about ATAGS
> > > > > and we really don't need to reserve those on arm64.
> > > > 
> > > > Commit 2359fa7a878 disables the entire arch_lmb_reserve function on
> > > > aarch64, yes.  I assumed when we had talked that it was a small area
> > > > being set aside and perhaps mis-recalled that ATAGS tended to live at
> > > > DDR_BASE + 0x800 or so.
> > > 
> > > That arch_lmb_reserve() is responsible for reserving architecture specific
> > > memory. On arm32 it is ATAGS, on arm64 it is nothing as far as I can tell
> > > (and see below regarding the TLB).
> > 
> > I don't think that LMB ever covered ATAGS.  ATAGS, I could have sworn,
> > were at start of memory + 0x800 or so.  This LMB is for the top of
> > memory where U-Boot is.
> 
> What is there to protect which Linux does not set up again ?

What does Linux have to do this with?  I don't see, but maybe have
missed, where "U-Boot adds memory region to internal LMB list" is
translated to "Update the device tree Linux will have with these
regions".  I do see code to read the reserved-memory regions from a DTB
and add them to our LMB, but not the other direction.

-- 
Tom

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