[U-Boot] [PATCH v 1/3] arm: do not force d-cache enable on all boards

[Albert ARIBAUD]

Hi Aneesh,

Le 05/08/2011 17:07, Aneesh V a écrit :
> Hi Albert,
>
> On Monday 01 August 2011 04:48 PM, Aneesh V wrote:
>> c2dd0d45540397704de9b13287417d21049d34c6 added dcache_enable()
>> to board_init_r(). This enables d-cache for all ARM boards.
>> As a result some of the arm boards that are not cache-ready
>> are broken. Revert this change and allow platform code to
>> take the decision on d-cache enabling.
>>
>> Also add some documentation for cache usage in ARM.
>>
>> Signed-off-by: Aneesh V<aneesh at ti.com>
>> ---
>> MAKEALL pending. Will update the results tomorrow.
>> ---
>> arch/arm/lib/board.c | 8 +++-----
>> arch/arm/lib/cache.c | 12 ++++++++++++
>> doc/README.arm-caches | 40 ++++++++++++++++++++++++++++++++++++++++
>> include/common.h | 1 +
>> 4 files changed, 56 insertions(+), 5 deletions(-)
>> create mode 100644 doc/README.arm-caches
>>
>> diff --git a/arch/arm/lib/board.c b/arch/arm/lib/board.c
>> index 90709d0..d093d5b 100644
>> --- a/arch/arm/lib/board.c
>> +++ b/arch/arm/lib/board.c
>> @@ -446,11 +446,9 @@ void board_init_r (gd_t *id, ulong dest_addr)
>> gd->flags |= GD_FLG_RELOC; /* tell others: relocation done */
>>
>> monitor_flash_len = _end_ofs;
>> - /*
>> - * Enable D$:
>> - * I$, if needed, must be already enabled in start.S
>> - */
>> - dcache_enable();
>> +
>> + /* Enable caches */
>> + enable_caches();
>>
>> debug ("monitor flash len: %08lX\n", monitor_flash_len);
>> board_init(); /* Setup chipselects */
>> diff --git a/arch/arm/lib/cache.c b/arch/arm/lib/cache.c
>> index 92b61a2..b545fb7 100644
>> --- a/arch/arm/lib/cache.c
>> +++ b/arch/arm/lib/cache.c
>> @@ -53,3 +53,15 @@ void __flush_dcache_all(void)
>> }
>> void flush_dcache_all(void)
>> __attribute__((weak, alias("__flush_dcache_all")));
>> +
>> +
>> +/*
>> + * Default implementation of enable_caches()
>> + * Real implementation should be in platform code
>> + */
>> +void __enable_caches(void)
>> +{
>> + puts("WARNING: Caches not enabled\n");
>> +}
>> +void enable_caches(void)
>> + __attribute__((weak, alias("__enable_caches")));
>> diff --git a/doc/README.arm-caches b/doc/README.arm-caches
>> new file mode 100644
>> index 0000000..9edc252
>> --- /dev/null
>> +++ b/doc/README.arm-caches
>> @@ -0,0 +1,40 @@
>> +Disabling I-cache:
>> +- Set CONFIG_SYS_ICACHE_OFF
>> +
>> +Disabling D-cache:
>> +- Set CONFIG_SYS_DCACHE_OFF
>> +
>> +Enabling I-cache:
>> +- Make sure CONFIG_SYS_ICACHE_OFF is not set and call icache_enable().
>> +
>> +Enabling D-cache:
>> +- Make sure CONFIG_SYS_ICACHE_OFF is not set and call dcache_enable().
>> +
>> +Enabling Caches at System Startup:
>> +- Implement enable_caches() for your platform and enable the I-cache and
>> + D-cache from this function. This function is called immediately
>> + after relocation.
>> +
>> +Guidelines for Working with D-cache:
>> +
>> +Memory to Peripheral DMA:
>> +- Flush the buffer after the MPU writes the data and before the DMA is
>> + initiated.
>> +
>> +Peripheral to Memory DMA:
>> +- Invalidate the buffer after the DMA is complete and before the MPU
>> reads
>> + it.
>
> The other discussion we are having about caches made me realize that I
> need to improve the above guideline like this:
>
> Peripheral to Memory DMA:
> - Invalidate the buffer before starting the DMA(This is for preventing
> cache-line replacements from corrupting the DMA buffer during the
> course of DMA).

Correct, but maybe you should indicate why this happens (not all people 
will realize that some *other* use of the cache might cause eviction of 
a cache line, thus a possible unexpected flush).

> - Invalidate the buffer after the DMA is complete and before the MPU
> reads it.
>
> I shall submit an updated patch for this.

Thanks!

> best regards,
> Aneesh

Amicalement,
-- 
Albert.