[U-Boot] [PATCH v4] nios2: convert dma_alloc_coherent to use malloc_cache_aligned

[Thomas Chou <thomas@wytron.com.tw>]

Hi  Marek,

On 10/12/2015 09:46 PM, Marek Vasut wrote:
> On Monday, October 12, 2015 at 02:55:03 PM, Thomas Chou wrote:
>> Hi Marek,
>
> Hi Thomas,
>
>> On 10/12/2015 06:32 PM, Marek Vasut wrote:
>>> Wouldn't invalidate_dcache_range() be enough here ? You don't care about
>>> the data in the newly allocated area at this point I guess -- either you
>>> fill them in and then flush, for DMA from CPU to device OR you receive
>>> data from device to CPU and then you invalidate this buffer again.
>>
>> No. We cannot use invalidate cache here. This is related to cache design
>> of nios2, kind of direct mapped cache.
>
> Can you please expand on this ?

This is rather hardware depended.

Please refer to page 7 about cache implementation on the "Nios II Core 
Implementation Detail" manual,

https://www.altera.com/content/dam/altera-www/global/en_US/pdfs/literature/hb/nios2/n2cpu_nii51015.pdf

And page 227, 8-44 about initd and initda instructions on the "Nios II 
Classic Processor Reference Guide",

https://www.altera.com/content/dam/altera-www/global/en_US/pdfs/literature/hb/nios2/n2cpu_nii5v1.pdf

The initda instruction might do the job. But nios2 cpu with 4 bytes 
dcache line size does not support this instruction. So we don't 
implement the invalidate_dcache_range/all() in u-boot yet.

Of course, we can add the invalidate cache ops if we can drop the 
support of nios2 cpu with 4 bytes dcache line size.

>
> btw. I was thinking about this whole cache situation. Please don't get me wrong,
> my intention is not to put way more work unto you and/or grind you about minor
> details. I hope it doesn't look that way to you.

No worries. It is just that I had very little free time last night to 
give more details. You are welcome.

Best regards,
Thomas