From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Brezillon Subject: Re: [PATCH v4 6/7] mtd: nand: omap2: Fix high memory dma prefetch transfer Date: Mon, 21 Mar 2016 16:04:43 +0100 Message-ID: <20160321160443.0a4165d1@bbrezillon> References: <1457654203-20856-1-git-send-email-fcooper@ti.com> <1457654203-20856-7-git-send-email-fcooper@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1457654203-20856-7-git-send-email-fcooper-l0cyMroinI0@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Franklin S Cooper Jr Cc: nsekhar-l0cyMroinI0@public.gmane.org, dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, computersforpeace-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, rogerq-l0cyMroinI0@public.gmane.org, tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org Hi Franklin, On Thu, 10 Mar 2016 17:56:42 -0600 Franklin S Cooper Jr wrote: > Based on DMA documentation and testing using high memory buffer when > doing dma transfers can lead to various issues including kernel > panics. I guess it all comes from the vmalloced buffer case, which are not guaranteed to be physically contiguous (one of the DMA requirement, unless you have an iommu). > > To workaround this simply use cpu copy. The amount of high memory > buffers used are very uncommon so no noticeable performance hit should > be seen. Hm, that's not necessarily true. UBI and UBIFS allocate their buffers using vmalloc (vmalloced buffers fall in the high_memory region), and those are likely to be dis-contiguous if you have NANDs with pages > 4k. I recently posted patches to ease sg_table creation from any kind of virtual address [1][2]. Can you try them and let me know if it fixes your problem? Thanks, Boris [1]https://lkml.org/lkml/2016/3/8/276 [2]https://lkml.org/lkml/2016/3/8/277 -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html