From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH] mtd: m25p80: make command buffer DMA-safe From: Artem Bityutskiy To: Johannes Stezenbach In-Reply-To: <20091103100018.GA20519@sig21.net> References: <20091028132137.GA17813@sig21.net> <1257230165.21596.33.camel@localhost> <20091103100018.GA20519@sig21.net> Content-Type: text/plain; charset="UTF-8" Date: Tue, 10 Nov 2009 16:54:07 +0200 Message-Id: <1257864847.21596.769.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Cc: linux-mtd@lists.infradead.org, David Brownell , David Woodhouse , linux-kernel@vger.kernel.org Reply-To: dedekind1@gmail.com List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2009-11-03 at 11:00 +0100, Johannes Stezenbach wrote: > 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. Pushed to my l2-mtd-2.6 tree, thanks. -- Best Regards, Artem Bityutskiy (Артём Битюцкий)