[PATCH] testsuite/spcache01: Clear allocated coherent cache memory

[Christian MAUDERER]

Am 19.10.21 um 16:48 schrieb Sebastian Huber:
> 
> 
> On 18/10/2021 23:08, Chris Johns wrote:
>> On 18/10/21 8:37 pm, Sebastian Huber wrote:
>>> On 18/10/2021 09:53, Chris Johns wrote:
>>>> On 18/10/21 4:50 pm, Sebastian Huber wrote:
>>>>> On 18/10/2021 07:19,chrisj at rtems.org   wrote:
>>>>>> From: Chris Johns<chrisj at rtems.org>
>>>>>>
>>>>>> - Coherent cache memory is used in libbsd for things like descriptors
>>>>>>      and it optionally clears the memory on allocation. Test is 
>>>>>> works.
>>>>> There is no guarantee that memset() and memcpy() work with cache 
>>>>> coherent
>>>>> memory. Such memory areas may disallow misaligned access for example.
>>>> That seems reasonable however this change about testing the implicit
>>>> requirements we have that memset works. LibBSD requires memset works 
>>>> ...
>>>>
>>>> https://git.rtems.org/rtems-libbsd/tree/rtemsbsd/rtems/rtems-kernel-bus-dma.c?h=6-freebsd-12#n260 
>>>>
>>>>
>>> Using memset() here could be a bug in libbsd.
>> Yes, I also think so.
>>
>> But what is a suitable mechanism to make sure the arch or BSP handle it
>> correctly? Maybe a clear routine in libbsd using the bus space API? That
>> interface has to work or the drivers will not work.
> 
> I think we had similar issues on another BSP. Christian, do you remember 
> how we solved this?
> 

I remember mainly problems with copying memory. I think the last time it 
resulted in an ugly "copy_from/to_io" function on the atsam:

   https://git.rtems.org/rtems/tree/bsps/arm/atsam/start/iocopy.c

The bus_space_* functions should work. Only problem is that a valid 
bus_space_tag is missing in this context. I think x86 uses it. I think 
for all other platforms it is unused.

Best regards

Christian
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