Re: [PATCH] powerpc 8xx: Fixing memory init issue with CONFIG_PIN_TLB
From: leroy christophe
Date: Wed Oct 16 2013 - 01:45:44 EST
Le 15/10/2013 22:33, Scott Wood a Ãcrit :
On Tue, 2013-10-15 at 18:27 +0200, leroy christophe wrote:
Le 11/10/2013 17:13, Joakim Tjernlund a Ãcrit :
"Linuxppc-dev"
<linuxppc-dev-bounces+joakim.tjernlund=transmode.se@xxxxxxxxxxxxxxxx>
wrote on 2013/10/11 14:56:40:
Activating CONFIG_PIN_TLB allows access to the 24 first Mbytes of memory
at
bootup instead of 8. It is needed for "big" kernels for instance when
activating
CONFIG_LOCKDEP_SUPPORT. This needs to be taken into account in init_32
too,
otherwise memory allocation soon fails after startup.
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
diff -ur linux-3.11.org/arch/powerpc/kernel/head_8xx.S
linux-3.11/arch/powerpc/kernel/head_8xx.S
--- linux-3.11.org/arch/powerpc/mm/init_32.c 2013-09-02
22:46:10.000000000 +0200
+++ linux-3.11/arch/powerpc/mm/init_32.c 2013-09-09 11:28:54.000000000
+0200
@@ -213,7 +213,12 @@
*/
BUG_ON(first_memblock_base != 0);
+#ifdef CONFIG_PIN_TLB
+ /* 8xx can only access 24MB at the moment */
+ memblock_set_current_limit(min_t(u64, first_memblock_size,
0x01800000));
+#else
/* 8xx can only access 8MB at the moment */
memblock_set_current_limit(min_t(u64, first_memblock_size,
0x00800000));
+#endif
}
#endif /* CONFIG_8xx */
hmm, I think you should always map 24 MB (or less if RAM < 24 MB) and do
the same
in head_8xx.S.
Or to keep it simple, just always map at least 16 MB here and in
head_8xx.S, assuming
that 16 MB is min RAM for any 8xx system running 3.x kernels.
Yes we could do a more elaborated modification in the future. However it
also has an impact on the boot loader, so I'm not sure we should make it
the default without thinking twice.
In the meantime, my patch does take into account the existing situation
where you have 8Mb by default and 24Mb when you activate CONFIG_PIN_TLB.
I see it as a bug fix and I believe we should include it at least in
order to allow including in the stable releases.
Do you see any issue with this approach ?
The patch is fine, but I don't think it's stable material (BTW, if it
were, you should have marked it as such when submitting). If I
understand the situation correctly, there's no regression, and nothing
fails to work with CONFIG_PIN_TLB that would have worked without it.
It's just making CONFIG_PIN_TLB more useful.
Yes the patch is definitly stable. How should I have mark it ?
The situation is that in 2010, I discovered that I was not able to start
a big Kernel because of the 8Mb limit.
You told me (see attached mail) that in order to get rid of that limit I
shall use CONFIG_PIN_TLB: it was the first step, it helped pass the
memory zeroize at init, but it was not enough as I then got problems
with the Device Tree being erased because being put inside the first 8Mb
area too. Then I temporarely gave up at that time.
Recently I started again. After fixing my bootloader to get the device
tree somewhere else, I discovered this 8Mb limit hardcoded in
mm/init_32.c for the 8xx
With the patch I submitted I can now boot a kernel which is bigger than 8Mb.
So, I'm a bit lost here on what to do.
--- Begin Message ---
On Tue, 2013-10-15 at 18:27 +0200, leroy christophe wrote:
> Le 11/10/2013 17:13, Joakim Tjernlund a Ãcrit :
> > "Linuxppc-dev"
> > <linuxppc-dev-bounces+joakim.tjernlund=transmode.se@xxxxxxxxxxxxxxxx>
> > wrote on 2013/10/11 14:56:40:
> >> Activating CONFIG_PIN_TLB allows access to the 24 first Mbytes of memory
> > at
> >> bootup instead of 8. It is needed for "big" kernels for instance when
> > activating
> >> CONFIG_LOCKDEP_SUPPORT. This needs to be taken into account in init_32
> > too,
> >> otherwise memory allocation soon fails after startup.
> >>
> >> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> >>
> >> diff -ur linux-3.11.org/arch/powerpc/kernel/head_8xx.S
> > linux-3.11/arch/powerpc/kernel/head_8xx.S
> >> --- linux-3.11.org/arch/powerpc/mm/init_32.c 2013-09-02
> > 22:46:10.000000000 +0200
> >> +++ linux-3.11/arch/powerpc/mm/init_32.c 2013-09-09 11:28:54.000000000
> > +0200
> >> @@ -213,7 +213,12 @@
> >> */
> >> BUG_ON(first_memblock_base != 0);
> >>
> >> +#ifdef CONFIG_PIN_TLB
> >> + /* 8xx can only access 24MB at the moment */
> >> + memblock_set_current_limit(min_t(u64, first_memblock_size,
> > 0x01800000));
> >> +#else
> >> /* 8xx can only access 8MB at the moment */
> >> memblock_set_current_limit(min_t(u64, first_memblock_size,
> > 0x00800000));
> >> +#endif
> >> }
> >> #endif /* CONFIG_8xx */
> > hmm, I think you should always map 24 MB (or less if RAM < 24 MB) and do
> > the same
> > in head_8xx.S.
> >
> > Or to keep it simple, just always map at least 16 MB here and in
> > head_8xx.S, assuming
> > that 16 MB is min RAM for any 8xx system running 3.x kernels.
> Yes we could do a more elaborated modification in the future. However it
> also has an impact on the boot loader, so I'm not sure we should make it
> the default without thinking twice.
>
> In the meantime, my patch does take into account the existing situation
> where you have 8Mb by default and 24Mb when you activate CONFIG_PIN_TLB.
> I see it as a bug fix and I believe we should include it at least in
> order to allow including in the stable releases.
>
> Do you see any issue with this approach ?
The patch is fine, but I don't think it's stable material (BTW, if it
were, you should have marked it as such when submitting). If I
understand the situation correctly, there's no regression, and nothing
fails to work with CONFIG_PIN_TLB that would have worked without it.
It's just making CONFIG_PIN_TLB more useful.
-Scott
--- End Message ---