From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from claw.goop.org (claw.goop.org [74.207.240.146]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "*.goop.org", Issuer "Goop.org CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id AE4C9DE1CE for ; Fri, 22 May 2009 03:52:48 +1000 (EST) Message-ID: <4A1592CF.8000208@goop.org> Date: Thu, 21 May 2009 10:43:43 -0700 From: Jeremy Fitzhardinge MIME-Version: 1.0 To: Becky Bruce Subject: Re: [PATCH V2 2/3] powerpc: Add support for swiotlb on 32-bit References: <1242340949-16369-1-git-send-email-beckyb@kernel.crashing.org> <1242340949-16369-2-git-send-email-beckyb@kernel.crashing.org> <20090519142656T.fujita.tomonori@lab.ntt.co.jp> <19E48A70-3332-423C-ACAD-390F940EE81C@kernel.crashing.org> In-Reply-To: <19E48A70-3332-423C-ACAD-390F940EE81C@kernel.crashing.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: FUJITA Tomonori , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, Ian Campbell List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Becky Bruce wrote: >> >> >> If we have something like in arch/{x86|ia64|powerpc}/dma-mapping.h: >> >> static inline int is_buffer_dma_capable(struct device *dev, >> dma_addr_t addr, size_t size) >> >> then we don't need two checking functions, address_needs_mapping and >> range_needs_mapping. > > It's never been clear to me *why* we had both in the first place - if > you can explain this, I'd be grateful :) I was about to ask the same thing. It seems that range_needs_mapping should be able to do both jobs. I think range_needs_mapping came from the Xen swiotlb changes, and address_needs_mapping came from your powerpc changes. Many of the changes were exact overlaps; I think this was one of the few instances where there was a difference. We need a range check in Xen (rather than iterating over individual pages) because we want to check that the underlying pages are machine contiguous, but I think that's also sufficient to do whatever checks you need to do. The other difference is that is_buffer_dma_capable operates on a dma_addr_t, which presumes that you can generate a dma address and then test for its validity. For Xen, it doesn't make much sense to talk about the dma_addr_t for memory which isn't actually dma-capable; we need the test to be in terms of phys_addr_t. Given that the two functions are always called from the same place, that doesn't seem to pose a problem. So I think the unified function would be something like: int range_needs_mapping(struct device *hwdev, phys_addr_t addr, size_t size); which would be defined somewhere under asm/*.h. Would that work for powerpc? J