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SubjectRe: [RFC PATCH 1/7] riscv: Get rid of compile time logic with MAX_EARLY_MAPPING_SIZE
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On Sun, 22 Mar 2020 04:00:22 PDT (-0700), alex@ghiti.fr wrote:
> There is no need to compare at compile time MAX_EARLY_MAPPING_SIZE value
> with PGDIR_SIZE since MAX_EARLY_MAPPING_SIZE is set to 128MB which is less
> than PGDIR_SIZE that is equal to 1GB: that allows to simplify early_pmd
> definition.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
> arch/riscv/mm/init.c | 16 ++++------------
> 1 file changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 238bd0033c3f..18bbb426848e 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -247,13 +247,7 @@ static void __init create_pte_mapping(pte_t *ptep,
>
> pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
> pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
> -
> -#if MAX_EARLY_MAPPING_SIZE < PGDIR_SIZE
> -#define NUM_EARLY_PMDS 1UL
> -#else
> -#define NUM_EARLY_PMDS (1UL + MAX_EARLY_MAPPING_SIZE / PGDIR_SIZE)
> -#endif
> -pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);
> +pmd_t early_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
>
> static pmd_t *__init get_pmd_virt(phys_addr_t pa)
> {
> @@ -267,14 +261,12 @@ static pmd_t *__init get_pmd_virt(phys_addr_t pa)
>
> static phys_addr_t __init alloc_pmd(uintptr_t va)
> {
> - uintptr_t pmd_num;
> -
> if (mmu_enabled)
> return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>
> - pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
> - BUG_ON(pmd_num >= NUM_EARLY_PMDS);
> - return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
> + BUG_ON((va - PAGE_OFFSET) >> PGDIR_SHIFT);
> +
> + return (uintptr_t)early_pmd;
> }
>
> static void __init create_pmd_mapping(pmd_t *pmdp,

My specific worry here was that allyesconfig kernels are quite large, and that
dropping the code to handle large kernels would make it even harder to boot
them. That said, I can't actually get one to boot so I'm happy to just push
that off until later and drop the code we can't practically use.

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>

Thanks!

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