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

[Stefan Roese]

On 10/20/23 10:21, Chris Packham wrote:

On Fri, 20 Oct 2023, 7:18 pm Stefan Roese, <s...@denx.de <mailto:s...@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.pack...@gmail.com
    <mailto:judge.pack...@gmail.com>>

    I'm not 100% happy with this approach / workaround - still it fixes an
    issue on your board, so:

    Reviewed-by: Stefan Roese <s...@denx.de <mailto:s...@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.

Applied to u-boot-marvell/master

Thanks,
Stefan

    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

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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: s...@denx.de