From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from moutng.kundenserver.de ([212.227.126.186]:52466 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753232Ab1GFPAU (ORCPT ); Wed, 6 Jul 2011 11:00:20 -0400 From: Arnd Bergmann To: linux-arm-kernel@lists.infradead.org Subject: Re: [Linaro-mm-sig] [PATCH 6/8] drivers: add Contiguous Memory Allocator Date: Wed, 6 Jul 2011 16:59:45 +0200 Cc: Nicolas Pitre , "Russell King - ARM Linux" , "'Daniel Walker'" , "'Jonathan Corbet'" , "'Mel Gorman'" , "'Chunsang Jeong'" , linux-kernel@vger.kernel.org, "'Michal Nazarewicz'" , linaro-mm-sig@lists.linaro.org, "'Jesse Barker'" , "'Kyungmin Park'" , "'Ankita Garg'" , "'Andrew Morton'" , linux-mm@kvack.org, "'KAMEZAWA Hiroyuki'" , linux-media@vger.kernel.org References: <1309851710-3828-1-git-send-email-m.szyprowski@samsung.com> <20110706142345.GC8286@n2100.arm.linux.org.uk> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201107061659.45253.arnd@arndb.de> List-ID: Sender: On Wednesday 06 July 2011, Nicolas Pitre wrote: > On Wed, 6 Jul 2011, Russell King - ARM Linux wrote: > > > Another issue is that when a platform has restricted DMA regions, > > they typically don't fall into the highmem zone. As the dmabounce > > code allocates from the DMA coherent allocator to provide it with > > guaranteed DMA-able memory, that would be rather inconvenient. > > Do we encounter this in practice i.e. do those platforms requiring large > contiguous allocations motivating this work have such DMA restrictions? You can probably find one or two of those, but we don't have to optimize for that case. I would at least expect the maximum size of the allocation to be smaller than the DMA limit for these, and consequently mandate that they define a sufficiently large CONSISTENT_DMA_SIZE for the crazy devices, or possibly add a hack to unmap some low memory and call dma_declare_coherent_memory() for the device. Arnd