From: Boris Brezillon Subject: Re: [PATCH 1/3] crypto: marvell/cesa - replace dma_to_phys with dma_map_single Date: Fri, 18 Mar 2016 10:30:28 +0100 Message-ID: <20160318103028.4be15b78@bbrezillon> References: <1458252137-24497-1-git-send-email-okaya@codeaurora.org> <20160317225459.GA19428@n2100.arm.linux.org.uk> <80402e2f82651814b1411a25b1740288@codeaurora.org> <20160317235020.GB19428@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: okaya@codeaurora.org, linux-arm-kernel@lists.infradead.org, timur@codeaurora.org, cov@codeaurora.org, nwatters@codeaurora.org, Herbert Xu , Arnaud Ebalard , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, "David S. Miller" To: Russell King - ARM Linux Return-path: Received: from down.free-electrons.com ([37.187.137.238]:40659 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756747AbcCRJac (ORCPT ); Fri, 18 Mar 2016 05:30:32 -0400 In-Reply-To: <20160317235020.GB19428@n2100.arm.linux.org.uk> Sender: linux-crypto-owner@vger.kernel.org List-ID: On Thu, 17 Mar 2016 23:50:20 +0000 Russell King - ARM Linux wrote: > On Thu, Mar 17, 2016 at 07:17:24PM -0400, okaya@codeaurora.org wrote: > > What is the correct way? I don't want to write engine->sram_dma = sram > > Well, what the driver _is_ wanting to do is to go from a CPU physical > address to a device DMA address. phys_to_dma() looks like the correct > thing there to me, but I guess that's just an offset and doesn't take > account of any IOMMU that may be in the way. > > If you have an IOMMU, then the whole phys_to_dma() thing is a total > failure as it only does a linear translation, and there are no > interfaces in the kernel to take account of an IOMMU in the way. So, > it needs something designed for the job, implemented and discussed by > the normal methods of proposing a new cross-arch interface for drivers > to use. > > What I'm certain of, though, is that the change proposed in this patch > will break current users of this driver: virt_to_page() on an address > returned by ioremap() is completely undefined, and will result in > either a kernel oops, or if not poking at memory which isn't a struct > page, ultimately resulting in something that isn't SRAM being pointed > to by "engine->sram_dma". > Or we could just do engine->sram_dma = res->start; which is pretty much what the SRAM/genalloc code is doing already. -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com