[PATCH -next v6 05/10] arm: armv8: mmu: add mem_map_fix_dram_banks

[Ilias Apalodimas]

On Fri, 12 Sept 2025 at 09:38, Anshul Dalal <anshuld at ti.com> wrote:
>
> Hi Ilias,
>
> On Fri Sep 12, 2025 at 12:03 PM IST, Ilias Apalodimas wrote:
> > Hi Anshul,
> >
> > On Fri, 5 Sept 2025 at 11:19, Anshul Dalal <anshuld at ti.com> wrote:
> >>
> >> For armv8, U-Boot uses a static map defined as 'mem_map' for configuring
> >> the MMU as part of mmu_setup.
> >>
> >> But since the exact configuration of memory banks might not be known at
> >> build time, many platforms such as imx9, versal2 etc. utilize
> >> gd->bd->bi_dram to configure the static map at runtime.
> >>
> >> Therefore this patch adds a new API mem_map_fix_dram_banks that modifies
> >> the static map in a similar way. Allowing for anyone to map all dram
> >> banks by just passing the index to last entry in their mem_map and it's
> >> length.
> >>
> >> Signed-off-by: Anshul Dalal <anshuld at ti.com>
> >> ---
> >>  arch/arm/cpu/armv8/cache_v8.c    | 27 +++++++++++++++++++++++++++
> >>  arch/arm/include/asm/armv8/mmu.h | 10 ++++++++++
> >>  2 files changed, 37 insertions(+)
> >>
> >> diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
> >> index 6e662395a83..edb895da1f2 100644
> >> --- a/arch/arm/cpu/armv8/cache_v8.c
> >> +++ b/arch/arm/cpu/armv8/cache_v8.c
> >> @@ -58,6 +58,33 @@ static int get_effective_el(void)
> >>         return el;
> >>  }
> >>
> >> +int mem_map_fix_dram_banks(unsigned int index, unsigned int len, u64 attrs)
> >> +{
> >> +       unsigned int i;
> >> +       int ret = fdtdec_setup_memory_banksize();
> >> +
> >> +       if (ret) {
> >> +               printf("%s: Failed to setup dram banks\n", __func__);
> >> +               return ret;
> >> +       }
> >> +
> >> +       if (index + CONFIG_NR_DRAM_BANKS >= len) {
> >> +               printf("%s: Not sufficient space in memory map\n", __func__);
> >> +               return -ENOMEM;
> >> +       }
> >
> > The length of the mem_map array is configured at compile time.
> > So this is going to fail for all existing boards unless someone
> > explicitly changes the size of their struct mm_region.
> > I think if we go down that path, we need to change the error message
> > as well and point them to the right direction
> >
> >> +
> >> +       for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {
> >> +               mem_map[index].virt = gd->bd->bi_dram[i].start;
> >> +               mem_map[index].phys = gd->bd->bi_dram[i].start;
> >> +               mem_map[index].size = gd->bd->bi_dram[i].size;
> >> +               mem_map[index].attrs = attrs;
> >> +               index++;
> >> +       }
> >> +
> >> +       mem_map[index] = (const struct mm_region){ 0 };
> >
> > Why do you need the const?
> > Can we do
> > memset(&mem_map[index], 0, sizeof(mem_map[index]));
> > instead?
> >
>
> Yeah, we could do that instead. But it essentially achieves the same
> thing, right?

Yes, i just find it a bit easier to read

Cheers
/Ilias
>
> Regards,
> Anshul