linux-kernel - Re: CMA on arm from zero address

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Date:	Fri, 10 Feb 2012 11:15:56 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: CMA on arm from zero address

Russell King - ARM Linux wrote:
> On Wed, Feb 08, 2012 at 02:21:26PM +0100, Michal Simek wrote:
>> First of all I have found how to do it (by CONFIG_PHYS_OFFSET) so the
>> problem is in QEMU.
> 
> So you're basically not telling the kernel about the first 32MB of memory.

It is not a problem.

> 
>> Currently experimenting how to convince CMA to allocate that memory for
>> my purpose.
> 
> Which means it won't be part of the kernels normal memory map, and so
> won't be in the page pool.  So CMA won't be able to help.
> 
> Instead, just ignore the first 32MB of RAM, and map it like any other
> peripheral to gain access to it.  You might need to use ioremap_wc()
> to avoid treating the memory as a 'device type' in ARMv6+.

I switched from cma to dma_declare_coherent_memory which does exactly what I wanted to
do.

Thanks,
Michal


-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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