Re: [PATCH v2 22/34] ARM: mmu32: create alloc_pte()

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 17.05.23 11:03, Sascha Hauer wrote:
> This is a preparation for using two level page tables in the PBL.
> To do that we need a way to allocate page tables in PBL. As malloc
> is not available in PBL, implement a function to allocate a page table
> from the area we also place the TTB.
> 
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---
>  arch/arm/cpu/mmu_32.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/cpu/mmu_32.c b/arch/arm/cpu/mmu_32.c
> index 4050d96846..a82382ad1e 100644
> --- a/arch/arm/cpu/mmu_32.c
> +++ b/arch/arm/cpu/mmu_32.c
> @@ -76,6 +76,27 @@ static bool pgd_type_table(u32 pgd)
>  	return (pgd & PMD_TYPE_MASK) == PMD_TYPE_TABLE;
>  }
>  
> +#define PTE_SIZE       (PTRS_PER_PTE * sizeof(u32))
> +
> +#ifdef __PBL__
> +static uint32_t *alloc_pte(void)
> +{
> +	static unsigned int idx = 3;

Can you add a comment explaining the choice of initial index?

> +
> +	idx++;

I know it's a quite construed example, but if one calls alloc_pte
often enough, it will start returning non-NULL pointers after
having returned NULL before. 

> +
> +	if (idx * PTE_SIZE >= ARM_EARLY_PAGETABLE_SIZE)
> +		return NULL;
> +
> +	return (void *)ttb + idx * PTE_SIZE;

To address above point, just replace idx with idx++ (and 3 with 4?).

> +}
> +#else
> +static uint32_t *alloc_pte(void)
> +{
> +	return xmemalign(PTE_SIZE, PTE_SIZE);
> +}
> +#endif
> +
>  static u32 *find_pte(unsigned long adr)
>  {
>  	u32 *table;
> @@ -125,8 +146,7 @@ static u32 *arm_create_pte(unsigned long virt, uint32_t flags)
>  
>  	virt = ALIGN_DOWN(virt, PGDIR_SIZE);
>  
> -	table = xmemalign(PTRS_PER_PTE * sizeof(u32),
> -			  PTRS_PER_PTE * sizeof(u32));
> +	table = alloc_pte();
>  
>  	if (!ttb)
>  		arm_mmu_not_initialized_error();

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