From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx138.postini.com [74.125.245.138]) by kanga.kvack.org (Postfix) with SMTP id D388B6B002B for ; Tue, 16 Oct 2012 22:26:08 -0400 (EDT) Received: by mail-wg0-f45.google.com with SMTP id dq12so5103952wgb.26 for ; Tue, 16 Oct 2012 19:26:07 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1350398501.2532.12.camel@dabdike> References: <1350192523.10946.4.camel@gitbox> <1350246895.11504.6.camel@gitbox> <20121015094547.GC29125@suse.de> <1350325704.31162.16.camel@gitbox> <1350398501.2532.12.camel@dabdike> Date: Wed, 17 Oct 2012 10:26:07 +0800 Message-ID: Subject: Re: dma_alloc_coherent fails in framebuffer From: Bob Liu Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: James Bottomley Cc: Tony Prisk , Mel Gorman , linux-mm@kvack.org, Arm Kernel Mailing List , Arnd Bergmann On Tue, Oct 16, 2012 at 10:41 PM, James Bottomley wrote: > On Tue, 2012-10-16 at 10:17 +0800, Bob Liu wrote: >> I think you need to declare that memory using >> dma_declare_coherent_memory() before >> alloc_from_coherent. > > This isn't true. Almost every platform has a mechanism for > manufacturing coherent memory (in the worst case, they just turn off the > CPU cache on a page and hand it out). The purpose of > dma_declare_coherent_memory() is to allow a per device declaration of > preferred regions ... usually because they reside either on the fast > path to the device or sometimes on the device itself. There are only a > handful of devices which need it, so in the ordinary course of events, > dma_alloc_coherent() is used without any memory declaration. > Sorry for my ambiguity. It obviously true we can use dma_alloc_coherent() without any memory declaration. I thought Tony's original idea was want to make dma_alloc_from_coherent() return success. But the dev->dma_mem check can't pass, so i suggested him using dma_declare_coherent_memory() to declare per-device area first. Thanks, --Bob -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org