linux-kernel - Re: [Q] block / zynq: DMA bouncing

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Message-ID: <52E69E1E.3020202@monstr.eu>
Date:	Mon, 27 Jan 2014 18:57:50 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [Q] block / zynq: DMA bouncing

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

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform



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