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
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