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

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

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