linux-kernel - Re: [PATCH] mtd: m25p80: make command buffer DMA-safe

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20091103100018.GA20519@sig21.net>
Date:	Tue, 3 Nov 2009 11:00:18 +0100
From:	Johannes Stezenbach <js@...21.net>
To:	Artem Bityutskiy <dedekind1@...il.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: m25p80: make command buffer DMA-safe

On Tue, Nov 03, 2009 at 08:36:05AM +0200, Artem Bityutskiy wrote:
> On Wed, 2009-10-28 at 14:21 +0100, Johannes Stezenbach wrote:
> > spi_write() requires the buffer to be DMA-safe, kmalloc()
> > it seperately to ensure this.
> 
> Even though it is just 4 or 5 bytes it can do DMA? Does not sound too
> sane to use DMA in that case. Does this patch fix a real error?
> 
> I do not know much about SPI, but for me it sounds like there should be
> a method to ask SPI to avoid using DMA, and you should use that method.

It fixes a real error -- with an out-of-tree driver and ancient kernel.
For the flash read/write case it is used with list-DMA (e.g. write 4 bytes,
read 64KB).  There are extensive comments in include/linux/spi/spi.h
which document the DMA-safe requirement of the buffers.

Thanks
Johannes
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/