From: vladimir.murzin@arm•com (Vladimir Murzin)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC v2 PATCH 0/3] Fix dma_alloc_coherent() and friends for NOMMU
Date: Tue, 13 Dec 2016 15:04:31 +0000 [thread overview]
Message-ID: <58500DFF.6010801@arm.com> (raw)
In-Reply-To: <1BE9400D-BACB-4C07-B6F0-1963D90A7029@esh.hu>
Hi,
On 13/12/16 14:33, Szemz? Andr?s wrote:
> Hi,
>
>> On 2016. Dec 13., at 14:45, Vladimir Murzin <vladimir.murzin@arm•com> wrote:
>>
>> Hi,
>>
>> It seem that addition of cache support for M-class cpus uncovered
>> latent bug in DMA usage. NOMMU memory model has been treated as being
>> always consistent; however, for R/M classes of cpu memory can be
>> covered by MPU which in turn might configure RAM as Normal
>> i.e. bufferable and cacheable. It breaks dma_alloc_coherent() and
>> friends, since data can stuck in caches now or be buffered.
>>
>> This patch set is trying to address the issue by providing region of
>> memory suitable for consistent DMA operations. It is supposed that such
>> region is marked by MPU as non-cacheable. Since we have MPU support in
>> Linux for R-class only and M-class setting MPU in bootloader, proposed
>> interface to advertise such memory is via "memdma=size at start" command
>> line option, to avoid clashing with normal memory (which usually comes
>> from dts) it'd be safer to use it together with "mem=" command line
>> option. Meanwhile, I'm open to suggestions for the better way telling
>> Linux of such memory.
>>
>
> I have tested these patches on my ATMEL SAME70 armv7m board.
>
> After setting the memory regions and attributes in the bootloader and providing the required
> command line parameters, the DMA issues fixed.
>
> I have tested an usart, sdcard, and ethernet driver with DMA enabled.
>
> Booting Linux on physical CPU 0x0
> Linux version 4.9.0 (root at debian) (gcc version 4.8.3 20140320 (prerelease) (Sourcery CodeBench Lite 2014.05-29) ) #4 Mon Dec 12 20:27:21 CET 201
> 6
> CPU: ARMv7-M [410fc271] revision 1 (ARMv7M), cr=00000000
> CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache
> OF: fdt:Machine model: SAME70-sampione board
> Built 1 zonelists in Zone order, mobility grouping on. Total pages: 15748
> Kernel command line: console=ttyS1,115200 root=/dev/mmcblk0p2 rw init=/linuxrc rootwait mem=62M memdma=2M at 0x73e00000
>
> So you can add my Tested-by.
>
> Thanks for the patches!
Glad to hear it works for you! Thanks for reporting and testing!
Cheers
Vladimir
>
> Regards,
> Andras
>
>
>
next prev parent reply other threads:[~2016-12-13 15:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-13 13:45 [RFC v2 PATCH 0/3] Fix dma_alloc_coherent() and friends for NOMMU Vladimir Murzin
2016-12-13 13:45 ` [RFC v2 PATCH 1/3] ARM: NOMMU: introduce dma operations for noMMU Vladimir Murzin
2017-01-02 15:26 ` Benjamin Gaignard
2017-01-04 10:33 ` Vladimir Murzin
2017-01-06 13:58 ` Benjamin Gaignard
2017-01-09 13:54 ` Vladimir Murzin
2016-12-13 13:45 ` [RFC v2 PATCH 2/3] ARM: NOMMU: set ARM_DMA_MEM_BUFFERABLE for M-class cpus Vladimir Murzin
2016-12-13 13:45 ` [RFC v2 PATCH 3/3] ARM: dma-mapping: remove traces of NOMMU code Vladimir Murzin
2016-12-13 14:07 ` [RFC v2 PATCH 0/3] Fix dma_alloc_coherent() and friends for NOMMU Russell King - ARM Linux
2016-12-13 14:14 ` Vladimir Murzin
2016-12-13 14:25 ` Robin Murphy
2016-12-13 15:02 ` Vladimir Murzin
2016-12-13 18:32 ` Robin Murphy
2016-12-14 10:15 ` Vladimir Murzin
2016-12-13 14:33 ` Szemző András
2016-12-13 15:04 ` Vladimir Murzin [this message]
2016-12-16 14:57 ` Alexandre Torgue
2016-12-16 15:00 ` Vladimir Murzin
2016-12-16 15:33 ` Alexandre Torgue
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