linux-kernel - Re: [PATCH v2 1/7] powerpc/8xx: Fix vaddr for IMMR early remap

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Message-ID: <1463440274.16584.123.camel@buserror.net>
Date:	Mon, 16 May 2016 18:11:14 -0500
From:	Scott Wood <oss@...error.net>
To:	Christophe Leroy <christophe.leroy@....fr>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 1/7] powerpc/8xx: Fix vaddr for IMMR early remap

On Fri, 2016-05-13 at 11:25 +0200, Christophe Leroy wrote:
> Le 11/05/2016 à 22:38, Scott Wood a écrit :
> > On Wed, 2016-05-11 at 17:03 +0200, Christophe Leroy wrote:
> > > Memory: 124428K/131072K available (3748K kernel code, 188K rwdata,
> > > 648K rodata, 508K init, 290K bss, 6644K reserved)
> > > Kernel virtual memory layout:
> > >    * 0xfffdf000..0xfffff000  : fixmap
> > >    * 0xfde00000..0xfe000000  : consistent mem
> > >    * 0xfddf6000..0xfde00000  : early ioremap
> > >    * 0xc9000000..0xfddf6000  : vmalloc & ioremap
> > > SLUB: HWalign=16, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
> > > 
> > > Today, IMMR is mapped 1:1 at startup
> > > 
> > > Mapping IMMR 1:1 is just wrong because it may overlap with another
> > > area. On most mpc8xx boards it is OK as IMMR is set to 0xff000000
> > > but for instance on EP88xC board, IMMR is at 0xfa200000 which
> > > overlaps with VM ioremap area
> > > 
> > > This patch fixes the virtual address for remapping IMMR with the fixmap
> > > regardless of the value of IMMR.
> > > 
> > > The size of IMMR area is 256kbytes (CPM at offset 0, security engine
> > > at offset 128k) so a 512k page is enough
> > > 
> > > Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> > > ---
> > > v2: No change
> > > 
> > >   arch/powerpc/include/asm/fixmap.h |  7 +++++++
> > >   arch/powerpc/kernel/asm-offsets.c |  8 ++++++++
> > >   arch/powerpc/kernel/head_8xx.S    | 11 ++++++-----
> > >   arch/powerpc/mm/mmu_decl.h        |  7 +++++++
> > >   arch/powerpc/sysdev/cpm_common.c  | 15 ++++++++++++---
> > >   5 files changed, 40 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/fixmap.h
> > > b/arch/powerpc/include/asm/fixmap.h
> > > index 90f604b..4508b32 100644
> > > --- a/arch/powerpc/include/asm/fixmap.h
> > > +++ b/arch/powerpc/include/asm/fixmap.h
> > > @@ -51,6 +51,13 @@ enum fixed_addresses {
> > >   	FIX_KMAP_BEGIN,	/* reserved pte's for temporary kernel
> > > mappings */
> > >   	FIX_KMAP_END = FIX_KMAP_BEGIN+(KM_TYPE_NR*NR_CPUS)-1,
> > >   #endif
> > > +#ifdef CONFIG_PPC_8xx
> > > +	/* For IMMR we need an aligned 512K area */
> > > +#define FIX_IMMR_SIZE	(512 * 1024 / PAGE_SIZE)
> > > +	FIX_IMMR_START,
> > > +	FIX_IMMR_BASE = __ALIGN_MASK(FIX_IMMR_START, FIX_IMMR_SIZE - 1)
> > > - 1 +
> > > +
> > > +		       FIX_IMMR_SIZE,
> > > +#endif
> > What happens if FIX_IMMR_START is, for example, 0x100?  Then
> > "__ALIGN_MASK(FIX_IMMR_START, FIX_IMMR_SIZE - 1) - 1" would be 0xff --
> > you've
> > gone backwards.  FIX_IMMR_BASE would be 0x17f, translating to an address
> > of
> > 0xffe80000.  IMMR would end at 0xfff00000.  The kmap range would begin at
> > 0xffeff000 and you'd have an overlap.
> > 
> > I think what you want is:
> > 	FIX_IMMR_BASE = (FIX_IMMR_START & ~(FIX_IMMR_SIZE - 1)) +
> > 			FIX_IMMR_SIZE - 1,
> > 
> Why would the kmap range begin at 0xffeff000 ?
> If FIX_IMMR_START is 0x100, this means FIX_KMAP_END is 0x0ff, so the 
> kmap range should begin at 0xfff00000, shouldn't it ?

Yeah, I'm not sure what I was thinking in that reply in general.

-Scott