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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Thu, 9 Dec 2021 11:12:13 +0100
Message-ID: <CAMj1kXEAQi58iXwoBoVHzqcM9EVU1O-_D+HaAVWpQYvjRYT+mg@mail.gmail.com>
Subject: Re: [PATCH v5 09/10] ARM: sunplus: Add initial support for Sunplus
 SP7021 SoC
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     =?UTF-8?B?cWluamlhblvopoPlgaVd?= <qinjian@cqplus1.com>,
        Rob Herring <robh+dt@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Mark Brown <broonie@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        DTML <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-clk <linux-clk@vger.kernel.org>,
        =?UTF-8?B?V2VsbHMgTHUg5ZGC6Iqz6aiw?= <wells.lu@sunplus.com>,
        Linus Walleij <linusw@kernel.org>
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On Thu, 9 Dec 2021 at 10:58, Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Thu, Dec 9, 2021 at 9:49 AM qinjian[=E8=A6=83=E5=81=A5] <qinjian@cqplu=
s1.com> wrote:
> > > On Tue, Dec 7, 2021 at 8:21 AM qinjian[=E8=A6=83=E5=81=A5] <qinjian@c=
qplus1.com> wrote:
> > > > > > @@ -152,6 +152,7 @@ textofs-$(CONFIG_ARCH_MSM8X60) :=3D 0x00208=
000
> > > > > >  textofs-$(CONFIG_ARCH_MSM8960) :=3D 0x00208000
> > > > > >  textofs-$(CONFIG_ARCH_MESON) :=3D 0x00208000
> > > > > >  textofs-$(CONFIG_ARCH_AXXIA) :=3D 0x00308000
> > > > > > +textofs-$(CONFIG_ARCH_SUNPLUS) :=3D 0x00308000
> > > > >
> > > > > What is this needed for? If it boots without this line, better av=
oid
> > > > > adding it, because
> > > > > it will increase the kernel size for everyone else (unless they a=
lso enable
> > > > > AXXIA).
> > > > >
> > > >
> > > > SP7021 reserved the 1st 1MB memory for ARM926@P-Chip using,
> > > > The 2nd 1MB memory for IOP device and the 3rd 1MB memory for bootlo=
ader.
> > > > I'll add these comments at next commit.
> > >
> > > I think you can just remove the memory from the system memory map in =
the
> > > device tree and pretend it only starts after the bootloader. It's bee=
n a while
> > > since I looked at this though, so I could be misremembering what the =
minimum
> > > boundaries are for doing this.
> >
> > I have test following 3 methods:
>
> Right, I was thinking of the third method here, which has the advantage o=
f
> not requiring the same odd base address for all other platforms, this
> is important to us.
> I don't see what the problem is with it in your example, does that mean y=
ou
> have a little less usable memory, or that something fails to work right? =
I don't
> know what the requirements are for memreserve.
>
> Adding a few more people to Cc, maybe they have ideas about how this
> was solved elsewhere.
>

The phys2virt patching now assumes a granularity of 2 MiB. This means
that by removing 3 MiB at the start of DRAM, you lose 1 MIB of usable
memory unless you find a way to memremap() it directly.

So I think a combination of the two approaches might work here
- remove 2 MiB from the the /memory node.
- add 1 MiB to the text offset instead of 3 MiB.

Note that this is a compromise, and still not our preferred approach.
It would be far better to move these reserved regions to the end of
DRAM instead.


>
> > 1. current patch
> > DT:
> >         memory {
> >                 reg =3D <0x00000000 0x20000000>; /* 512MB */
> >         };
> >
> >         reserved-memory {
> >                 #address-cells =3D <1>;
> >                 #size-cells =3D <1>;
> >                 ranges;
> >
> >                 iop_reserve: iop_device {
> >                         no-map;
> >                         reg =3D <0x00100000 0x00100000>;
> >                 };
> >                 a926_reserve: a926_memory {
> >                         no-map;
> >                         reg =3D <0x00000000 0x00100000>;
> >                 };
> >         };
> > arch/arm/Makefile:
> >         textofs-$(CONFIG_ARCH_SUNPLUS) :=3D 0x00308000
> >
> > bootlog & meminfo :
> > [    0.000000] Zone ranges:
> > [    0.000000]   Normal   [mem 0x0000000000000000-0x000000001fffffff]
> > [    0.000000] Movable zone start for each node
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x0000000000000000-0x00000000001fffff]
> > [    0.000000]   node   0: [mem 0x0000000000200000-0x000000001fffffff]
> > [    0.000000] Initmem setup node 0 [mem 0x0000000000000000-0x000000001=
fffffff]
> >
> > ~ # cat /proc/meminfo
> > MemTotal:         514008 kB
> > MemFree:          491960 kB
> > MemAvailable:     488608 kB
> >
> >
> >
> > 2. DT same as case 1, but no modify @ arch/arm/Makefile
> >
> > bootlog & meminfo :
> > [    0.000000] OF: fdt: Reserved memory: failed to reserve memory for n=
ode 'iop_device': base 0x00100000, size 1 MiB
> > [    0.000000] OF: fdt: Reserved memory: failed to reserve memory for n=
ode 'a926_memory': base 0x00000000, size 1 MiB
> > ...
> > [    0.000000] Zone ranges:
> > [    0.000000]   Normal   [mem 0x0000000000000000-0x000000001fffffff]
> > [    0.000000] Movable zone start for each node
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x0000000000000000-0x000000001fffffff]
> > [    0.000000] Initmem setup node 0 [mem 0x0000000000000000-0x000000001=
fffffff]
> >
> > ~ # cat /proc/meminfo
> > MemTotal:         516056 kB
> > MemFree:          493928 kB
> > MemAvailable:     490572 kB
> >
> >
> >
> > 3. DT:
> >         memory {
> >                 reg =3D <0x00300000 0x1FD00000>; /* 512 - 3 MB */
> >         };
> > no modify @ arch/arm/Makefile
> >
> > bootlog & meminfo :
> > [    0.000000] Zone ranges:
> > [    0.000000]   Normal   [mem 0x0000000000400000-0x000000001fffffff]
> > [    0.000000] Movable zone start for each node
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x0000000000400000-0x000000001fffffff]
> > [    0.000000] Initmem setup node 0 [mem 0x0000000000400000-0x000000001=
fffffff]
> >
> > ~ # cat /proc/meminfo
> > MemTotal:         511964 kB
> > MemFree:          489636 kB
> > MemAvailable:     486292 kB
> >
> >
> >
> > I think method 1 should be correct (compare method 2) & better (compare=
 method 3).
> >