[PATCH] arm: mvebu: AC5/AC5X: use fixed page table size

[Chris Packham]

On Fri, 20 Oct 2023, 7:18 pm Stefan Roese, <sr at denx.de> wrote:

> Hi Chris,
>
> On 10/18/23 22:53, Chris Packham wrote:
> > Since commit 6cdf6b7a340d ("arm64: Use FEAT_HAFDBS to track dirty pages
> > when available") the default get_page_table_size() sets some flags for
> > more efficient handling of dirty page table entries. This causes
> > problems on the AC5/AC5X SoC (specifically a lockup when calling
> > __asm_switch_ttbr() via mmu_set_region_dcache_behaviour()).
> >
> > The reason for the lockup isn't at all clear but it can be avoided if we
> > provide our own get_page_table_size() which stops gd->arch.has_hafdbs
> > from being set to true effectively returning the AC5/AC5X to the older
> > behaviour. This also opts for a simple fixed page table size rather than
> > trying to duplicate the more complicated logic to optimise the table
> > size.
> >
> > Signed-off-by: Chris Packham <judge.packham at gmail.com>
>
> I'm not 100% happy with this approach / workaround - still it fixes an
> issue on your board, so:
>
> Reviewed-by: Stefan Roese <sr at denx.de>
>

Yeah I'm not super happy about this either. But this is about the best I
could come up with.


> Perhaps you (or someone else) can look into this in more depth to get
> to the root of this issue at a later time.
>

I did spend a reasonable amount of time tracking down where things were
going wrong, even if I couldn't figure out why. The commit message
basically reflects what I found.


> Thanks,
> Stefan
>
> > ---
> >
> >   arch/arm/mach-mvebu/alleycat5/cpu.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/arch/arm/mach-mvebu/alleycat5/cpu.c
> b/arch/arm/mach-mvebu/alleycat5/cpu.c
> > index 8204d9627515..7ba57ae75e76 100644
> > --- a/arch/arm/mach-mvebu/alleycat5/cpu.c
> > +++ b/arch/arm/mach-mvebu/alleycat5/cpu.c
> > @@ -63,6 +63,11 @@ static struct mm_region ac5_mem_map[] = {
> >
> >   struct mm_region *mem_map = ac5_mem_map;
> >
> > +u64 get_page_table_size(void)
> > +{
> > +     return 0x80000;
> > +}
> > +
> >   void reset_cpu(void)
> >   {
> >   }
>
> Viele Grüße,
> Stefan Roese
>
> --
> DENX Software Engineering GmbH,      Managing Director: Erika Unter
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-51 Fax: (+49)-8142-66989-80 Email: sr at denx.de
>