[Q] block / zynq: DMA bouncing

[Guennadi Liakhovetski]

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:
> > On Mon, Jan 27, 2014 at 06:45:50PM +0100, Michal Simek wrote:
> >> 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.
> 
> > 
> > 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/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0001-Xilinx-ARM-BSP-prevent-DMA-into-lower-memory.patch
Type: text/x-diff
Size: 1867 bytes
Desc: 
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20140128/50003bc6/attachment.bin>