Re: [PATCH 1/2] MIPS: BMIPS: dts: remove unsupported entry for bcm7362

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Friday 08 May 2015 09:40:03 Kevin Cernekee wrote:
> On Fri, May 8, 2015 at 8:32 AM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
> > On Friday 08 May 2015 07:40:44 Kevin Cernekee wrote:
> >> On Fri, May 8, 2015 at 5:59 AM, Jaedon Shin <jaedon.shin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> > Remove unsupported memory entry for the bcm7362 platform. The BMIPS4380
> >> > processor only supports ZONE_NORMAL is not available for HIGHMEM.
> >> >
> >> > Signed-off-by: Jaedon Shin <jaedon.shin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> >> > ---
> >> >  arch/mips/boot/dts/brcm/bcm97362svmb.dts | 2 +-
> >> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >> >
> >> > diff --git a/arch/mips/boot/dts/brcm/bcm97362svmb.dts b/arch/mips/boot/dts/brcm/bcm97362svmb.dts
> >> > index b7b88e5dc9e7..ab8b01fa7dcf 100644
> >> > --- a/arch/mips/boot/dts/brcm/bcm97362svmb.dts
> >> > +++ b/arch/mips/boot/dts/brcm/bcm97362svmb.dts
> >> > @@ -8,7 +8,7 @@
> >> >
> >> >         memory@0 {
> >> >                 device_type = "memory";
> >> > -               reg = <0x00000000 0x10000000>, <0x20000000 0x30000000>;
> >> > +               reg = <0x00000000 0x10000000>;
> >>
> >> Hmm, this is more of a kernel limitation than a hardware limitation,
> >> though.  The board physically has 1GB of memory, right?  It is best if
> >> the DT entry reflects the actual hardware configuration.
> >>
> >> The Broadcom kernels enable the CPU's special "XKS01" feature to put
> >> 1GB of memory in ZONE_NORMAL:
> >>
> >> https://github.com/Broadcom/stblinux-3.3/tree/master/linux
> >>
> >
> > What exactly is the kernel limitation here?
> 
> If we can't enable HIGHMEM, e.g. because the MIPS CPU has D$ aliases,
> then Linux is supposed to ignore any RAM above the highmem/lowmem
> boundary.
> 
> There is code in paging_init() that tries to do this.  Several years
> ago it used to work, but the last time I tried it (~Oct 2014) it was
> broken due to some other changes in MIPS early memory init, so Linux
> hangs on boot unless you take the excess RAM out of DT.  Jaedon may be
> running into the same issue.

Ok, I see. Could you avoid the problem by not requiring highmem?

We have some hacks on arch/arm/mach-realview to provide a nonlinear
virt_to_phys() function, which ends up moving all RAM underneath the
lowmem limit.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html