Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932130AbZKRRrl (ORCPT ); Wed, 18 Nov 2009 12:47:41 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757667AbZKRRrl (ORCPT ); Wed, 18 Nov 2009 12:47:41 -0500 Received: from cantor.suse.de ([195.135.220.2]:43280 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757588AbZKRRrk (ORCPT ); Wed, 18 Nov 2009 12:47:40 -0500 Date: Wed, 18 Nov 2009 18:47:43 +0100 Message-ID: From: Takashi Iwai To: Ralf Baechle Cc: Thomas Bogendoerfer , Wu Zhangjin , Jaroslav Kysela , alsa-devel@alsa-project.org, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, Wu Zhangjin Subject: Re: [PATCH] MIPS: Fixups of ALSA memory maps In-Reply-To: <20091118142056.GB6615@linux-mips.org> References: <9cbcd06037c18288a6493459b8f3a6e1562eca77.1258389992.git.wuzhangjin@gmail.com> <20091116174324.GA17748@linux-mips.org> <20091118142056.GB6615@linux-mips.org> User-Agent: Wanderlust/2.15.6 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.7 Emacs/23.1 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3509 Lines: 90 At Wed, 18 Nov 2009 15:20:56 +0100, Ralf Baechle wrote: > > On Tue, Nov 17, 2009 at 10:29:10AM +0100, Takashi Iwai wrote: > > > > > Actually, this has been a looong-standing problem. > > > > I have a series of patches to fix these issues, but it's more > > > > intensively involved with dma_*() functions. > > > > > > > > The patches can be found in test/dma-fix branch of sound GIT tree. > > > > git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6.git test/dma-fix > > > > > > > > This basically adds dma_mmap_coherent() function to feasible > > > > architectures, which is already implemented for ARM, so far. > > > > > > Cool - but needs a little further tweaking to work right. That's a > > > solution which will use uncached accesses on all MIPS systems. > > > > > > IP27/IP35-family machines will explode when you try that. Eventually the > > > cache coherency logic will notice that cache, directory caches and memory > > > have become inconsistent and bombard the CPU with a bunch of nasty > > > exceptions. > > > > OK, that's really bad. > > Hardware designers do such things to you. Often even for a reason. Heh, not only software engineers are so crazy ;) > > > For cache-coherent machines otoh it's a big waste of performance. > > > > > > int dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma, > > > void *cpu_addr, dma_addr_t handle, size_t size) > > > { > > > struct page *pg; > > > > > > if (!plat_device_is_coherent(dev)) > > > vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > > > cpu_addr = (void *)dma_addr_to_virt(handle); > > > pg = virt_to_page(cpu_addr); > > > > > > return remap_pfn_range(vma, vma->vm_start, > > > page_to_pfn(pg) + vma->vm_pgoff, > > > size, vma->vm_page_prot); > > > } > > > EXPORT_SYMBOL(dma_mmap_coherent); > > > > > > Thomas - you're the IP28 specialist. Would the plat_device_is_coherent() > > > above have to become a cpu_is_noncoherent_r10000() call? Any further > > > nasties? > > > > Thanks for checking! > > You're welcome! > > So basically I'd not mind putting this into the Linux/MIPS tree; we still > can iron out the kinks from there on and probably much better than by > having arch stuff in the ALSA tree. Yes, that's the very purpose of my patchset. > I recall this new API having been posted for discussion to linux-arch. > What was the outcome? I'd only like to add a new API if the other arch > maintainers see it fit their needs also. Well, we haven't reached the consensus. The discussion faded away somehow mainly because I had too little time to update and ping people again. In Tokyo, I talked with some guys regarding this. Ben agreed to take this approach for ppc, and David said that he doesn't mind for sparc part. Fujita-san mentioned it's no big problem to add one op from the generic dma_ops. So, maybe somehow need to convince James in the end (and ask Paul to check SH part, too), then it'll be all up... theoretically :) Anyway, I'm going to raise the discussion again on linux-arch. I'm afraid it's a bit too late game for 2.6.33, but starting now is better than too late again. thanks, Takashi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/