[U-Boot] [PATCH] armv7:cache: D cache line size read method

[Aneesh V]

Hi Albert, Lukasz,

On Friday 12 August 2011 02:28 PM, Albert ARIBAUD wrote:
> Hi Lukasz,
>
> On 12/08/2011 10:24, Lukasz Majewski wrote:
>> This commit adds support for reading the D cache line size for armv7
>> architecture.
>>
>> The get_dcache_line_size() function is supposed to work in conjunction
>> with memalign call to provide D cache aligned DMA buffers.
>>
>> Signed-off-by: Lukasz Majewski<l.majewski at samsung.com>
>> Signed-off-by: Kyungmin Park<kyungmin.park at samsung.com>
>> CC: Aneesh V<aneesh at ti.com>
>> CC: Albert ARIBAUD<albert.u.boot at aribaud.net>
>> ---
>> arch/arm/cpu/armv7/cache_v7.c | 25 +++++++++++++++++++++++++
>> include/common.h | 1 +
>> 2 files changed, 26 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arm/cpu/armv7/cache_v7.c
>> b/arch/arm/cpu/armv7/cache_v7.c
>> index 3e1e1bf..bd0b1a8 100644
>> --- a/arch/arm/cpu/armv7/cache_v7.c
>> +++ b/arch/arm/cpu/armv7/cache_v7.c
>> @@ -246,6 +246,21 @@ static void v7_inval_tlb(void)
>> CP15ISB;
>> }
>>
>> +/* Read the cache line size (bytes) */
>> +static int v7_dcache_line_size(void)
>> +{
>> + u32 ccsidr, log2_line_len;
>> +
>> + ccsidr = get_ccsidr();
>> +
>> + log2_line_len = ((ccsidr& CCSIDR_LINE_SIZE_MASK)>>
>> + CCSIDR_LINE_SIZE_OFFSET) + 2;
>> + /* Converting from words to bytes */
>> + log2_line_len += 2;
>> +
>> + return 1<< log2_line_len;
>> +}
>> +
>> void invalidate_dcache_all(void)
>> {
>> v7_maint_dcache_all(ARMV7_DCACHE_INVAL_ALL);
>> @@ -303,6 +318,11 @@ void flush_cache(unsigned long start, unsigned
>> long size)
>> {
>> flush_dcache_range(start, start + size);
>> }
>> +
>> +int get_dcache_line_size(void)
>> +{
>> + return v7_dcache_line_size();
>> +}
>> #else /* #ifndef CONFIG_SYS_DCACHE_OFF */
>> void invalidate_dcache_all(void)
>> {
>> @@ -327,6 +347,11 @@ void arm_init_before_mmu(void)
>> void flush_cache(unsigned long start, unsigned long size)
>> {
>> }
>> +
>> +int get_dcache_line_size(void)
>> +{
>> + return 0;
>> +}
>> #endif /* #ifndef CONFIG_SYS_DCACHE_OFF */
>>
>> #ifndef CONFIG_SYS_ICACHE_OFF
>> diff --git a/include/common.h b/include/common.h
>> index 12a1074..b535300 100644
>> --- a/include/common.h
>> +++ b/include/common.h
>> @@ -622,6 +622,7 @@ void flush_dcache_range(unsigned long start,
>> unsigned long stop);
>> void invalidate_dcache_range(unsigned long start, unsigned long stop);
>> void invalidate_dcache_all(void);
>> void invalidate_icache_all(void);
>> +int get_dcache_line_size(void);
>>
>> /* arch/$(ARCH)/lib/ticks.S */
>> unsigned long long get_ticks(void);
>
> I like the idea of a global cache line accessor, but:
>
> 1) Does it have to be a function? I don't know cache implementations
> where line size is not a constant, and a function might be overkill.
>
> 2) If it has to be a function, then I'd rather have the function
> introduced in arch/arm/lib/cache.c as a weak function returning 32, with
> armv7 providing a replacement.

Since this is used from generic drivers I think this should be defined 
all ARCHs. How about something like this.

int __weak get_dcache_line_size(void)
{
#if  defined(CONFIG_SYS_CACHE_LINE_SIZE) && !defined(CONFIG_SYS_DCACHE_OFF)
	return CONFIG_SYS_CACHE_LINE_SIZE;
#else
	return sizeof(int); /* or 0 - whatever is appropriate for memalign() */
#endif
}

Then over-ride this from the respective ARCH implementation if there is
a cache-type registers. I see that armv5/6/7 all can find this at
run-time from CP15 registers.

>
> Aneesh, that patch could affect your patch series as the magic 32 could
> then come from this weak function rather than be hard-coded.

I think you are referring to Hong's series. In armv7 series we are
getting the size by reading ccsidr register just like Lukasz is doing
here - no magic values. I think in Hong's series also this can be found
from the cache type CP15 register.

br,
Aneesh