[Q] block / zynq: DMA bouncing

Hi Michal,

(trimmed CC a bit)

On Mon, 27 Jan 2014, Michal Simek wrote:

On 01/27/2014 06:52 PM, Russell King - ARM Linux wrote:

quoted

On Mon, Jan 27, 2014 at 06:45:50PM +0100, Michal Simek wrote:

quoted

Why 0x4000? IRC Linux for ARM is using space for any purpose.
Russell knows this much better than I.

Probably because as the kernel is loaded at 0x8000, it will place the
swapper page table at 0x4000, thus covering from 0x4000 upwards.

Ah yeah swapper.

quoted

Thus, the majority of your un-DMA-able memory will be kernel text or
swapper page tables.

Yes, exactly.
0x0 - 0x4000 - reserving not to be used by DMA
0x4000 - 0x8000 swapper page table
0x8000 - 0x80000 kernel text + up

Maybe you could submit something like the attached patch upstream. I'm not 
sure shom you'd like to put as its original author. I put John Linn there 
as he originally authored commit 5b9f3f2ac8a3e4edae9de7b855f25f757884d84c 
from Xilinx tree with the same description, as the attached patch. 
Unfortunately, that commit didn't have an Sob.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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