On Fri, May 18, 2018 at 1:41 PM, Sam Ravnborg <sam@xxxxxxxxxxxx> wrote:
> 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@xxxxxxxxx>
>> ---
>> 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.
>
The cost of find_pte() is two simple checks and an extra table lookup.
IMHO, seems like a trivial price to pay to avoid code duplication.
Thanks,
Andrey Smirnov
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