Re: [PATCH v3 24/28] ARM: mmu: Use find_pte() to find PTE in create_vector_table()

[Sam Ravnborg <sam@ravnborg.org>]

Hi Andrey.

On Thu, May 17, 2018 at 01:58:33PM -0700, Andrey Smirnov wrote:
> There's already a function that implement necessary arithemtic to find
> offset within page table for a given address, so make use of it
> instead of re-implementing it again.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> ---
>  arch/arm/cpu/mmu.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/cpu/mmu.c b/arch/arm/cpu/mmu.c
> index 21394deb1..f9e4d1a50 100644
> --- a/arch/arm/cpu/mmu.c
> +++ b/arch/arm/cpu/mmu.c
> @@ -272,8 +272,7 @@ static void create_vector_table(unsigned long adr)
>  {
>  	struct resource *vectors_sdram;
>  	void *vectors;
> -	u32 *exc;
> -	int idx;
> +	u32 *pte;
>  
>  	vectors_sdram = request_sdram_region("vector table", adr, PAGE_SIZE);
>  	if (vectors_sdram) {
> @@ -293,9 +292,9 @@ static void create_vector_table(unsigned long adr)
>  		vectors = xmemalign(PAGE_SIZE, PAGE_SIZE);
>  		pr_debug("Creating vector table, virt = 0x%p, phys = 0x%08lx\n",
>  			 vectors, adr);
> -		exc = arm_create_pte(adr, pte_flags_uncached);
> -		idx = (adr & (PGDIR_SIZE - 1)) >> PAGE_SHIFT;
> -		exc[idx] = (u32)vectors | PTE_TYPE_SMALL | pte_flags_cached;
> +		arm_create_pte(adr, pte_flags_uncached);
> +		pte = find_pte(adr);
> +		*pte = (u32)vectors | PTE_TYPE_SMALL | pte_flags_cached;

This looks more elegant, but the cost here is that
find_pte() is more expensive than the simple array
operations done before.

I am not sure if this is needed in followig patches,
it just looks a bit expensive.

	Sam

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