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From: Andrey Smirnov <andrew.smirnov@gmail.com>
To: Sam Ravnborg <sam@ravnborg.org>
Cc: Barebox List <barebox@lists.infradead.org>
Subject: Re: [PATCH v3 24/28] ARM: mmu: Use find_pte() to find PTE in create_vector_table()
Date: Fri, 18 May 2018 16:30:04 -0700	[thread overview]
Message-ID: <CAHQ1cqENkW2xjSFiQ2LAF9XdbJmB5M3ZxzFbhr_-qDaPq2VryA@mail.gmail.com> (raw)
In-Reply-To: <20180518204137.GC26895@ravnborg.org>

On Fri, May 18, 2018 at 1:41 PM, Sam Ravnborg <sam@ravnborg.org> 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@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.
>

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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  reply	other threads:[~2018-05-18 23:30 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-17 20:58 [PATCH v3 00/28] ARM MMU code improvements and on-demand PTE allocation Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 01/28] ARM: mmu: Remove unused ARM_VECTORS_SIZE Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 02/28] ARM: mmu: Make use of IS_ALIGNED in arm_mmu_remap_sdram() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 03/28] ARM: mmu: Use ALIGN and ALIGN_DOWN in map_cachable() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 04/28] ARM: mmu: Introduce set_ttbr() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 05/28] ARM: mmu: Introduce set_domain() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 06/28] ARM: mmu: Share code for create_sections() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 07/28] ARM: mmu: Separate index and address in create_sections() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 08/28] sizes.h: Sync with Linux 4.16 Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 09/28] ARM: mmu: Specify size in bytes in create_sections() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 10/28] ARM: mmu: Share code for initial flat mapping creation Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 11/28] ARM: mmu: Share PMD_SECT_DEF_CACHED Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 12/28] ARM: mmu: Drop needless shifting in map_io_sections() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 13/28] ARM: mmu: Replace hardcoded shifts with pgd_index() from Linux Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 14/28] ARM: mmu: Trivial simplification in arm_mmu_remap_sdram() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 15/28] ARM: mmu: Replace various SZ_1M with PGDIR_SIZE Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 16/28] ARM: mmu: Use PAGE_SIZE when specifying size of one page Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 17/28] ARM: mmu: Define and use PTRS_PER_PTE Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 18/28] ARM: mmu: Use PAGE_SIZE instead of magic right shift by 12 Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 19/28] ARM: mmu: Use xmemalign in arm_create_pte() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 20/28] ARM: mmu: Use xmemalign in mmu_init() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 21/28] ARM: mmu: Share code between dma_alloc_*() functions Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 22/28] ARM: mmu: Pass PTE flags a parameter to arm_create_pte() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 23/28] ARM: mmu: Make sure that address is 1M aligned in arm_create_pte() Andrey Smirnov
2018-05-18 20:23   ` Sam Ravnborg
2018-05-21 19:12     ` Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 24/28] ARM: mmu: Use find_pte() to find PTE in create_vector_table() Andrey Smirnov
2018-05-18 20:41   ` Sam Ravnborg
2018-05-18 23:30     ` Andrey Smirnov [this message]
2018-05-17 20:58 ` [PATCH v3 25/28] ARM: mmu: Use dma_inv_range() in dma_sync_single_for_cpu() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 26/28] ARM: mmu: Simplify the use of dma_flush_range() Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 27/28] ARM: mmu: Implement on-demand PTE allocation Andrey Smirnov
2018-05-17 20:58 ` [PATCH v3 28/28] ARM: mmu: Introduce ARM_TTB_SIZE Andrey Smirnov

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