[PATCH rtems 3/3] bsps/fdt: Make sure data is cache aligned.

[Christian Mauderer]

Hello Gedare,

thanks for the review.

On 17/07/2020 17:53, Gedare Bloom wrote:
> The other 2 BSP-specific patches look fine. I didn't look too closely
> at the imx-specific part.
> 
> On Thu, Jul 16, 2020 at 11:55 PM Christian Mauderer
> <christian.mauderer at embedded-brains.de> wrote:
>>
>> The cache of the fdt blob is flushed after copy. Therefore it should be
>> aligned.
>> ---
>>  bsps/shared/start/bsp-fdt.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/bsps/shared/start/bsp-fdt.c b/bsps/shared/start/bsp-fdt.c
>> index 7e8d8922a8..f55273e4ca 100644
>> --- a/bsps/shared/start/bsp-fdt.c
>> +++ b/bsps/shared/start/bsp-fdt.c
>> @@ -28,10 +28,10 @@
>>  #endif
>>
>>  #ifdef BSP_FDT_BLOB_READ_ONLY
>> -static const uint32_t
>> +static const uint32_t CPU_STRUCTURE_ALIGNMENT
> 
> Typically seen the alignment after the variable decl. Maybe it is
> flexible, but we might consider a rule for consistency if both
> placements work.

I'll move it.

> 
>>  bsp_fdt_blob[BSP_FDT_BLOB_SIZE_MAX / sizeof(uint32_t)] = { 0xdeadbeef };
>>  #else
>> -static uint32_t
>> +static uint32_t CPU_STRUCTURE_ALIGNMENT
>>  bsp_fdt_blob[BSP_FDT_BLOB_SIZE_MAX / sizeof(uint32_t)];
>>  #endif
>>
>> @@ -48,6 +48,7 @@ void bsp_fdt_copy(const void *src)
>>
>>    if (s != d) {
>>      size_t m = MIN(sizeof(bsp_fdt_blob), fdt_totalsize(src));
>> +    size_t aligned_size = ((m-1) | (CPU_CACHE_LINE_BYTES-1)) + 1;
> 
> This is a little bit of magic, I guess it works with cache line bytes
> a power of 2. Do we have a macro for this?
> 

I don't think that we have a macro for alignment. But I found a
"roundup2" in newlibs sys/param.h after some searching. I'll try to use
that one.

>>      size_t n = (m + sizeof(*d) - 1) / sizeof(*d);
>>      size_t i;
>>
>> @@ -55,7 +56,7 @@ void bsp_fdt_copy(const void *src)
>>        d[i] = s[i];
>>      }
>>
>> -    rtems_cache_flush_multiple_data_lines(d, m);
>> +    rtems_cache_flush_multiple_data_lines(d, aligned_size);
>>    }
>>  }
>>
>> --
>> 2.26.2
>>
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