From: Russell King - ARM Linux Subject: Re: [PATCH 6/9] crypto: ux500/cryp - Set DMA configuration though dma_slave_config() Date: Fri, 26 Apr 2013 10:41:23 +0100 Message-ID: <20130426094123.GG14496@n2100.arm.linux.org.uk> References: <1366280825-31136-1-git-send-email-lee.jones@linaro.org> <20130425134402.GN4623@gmail.com> <201304251611.39667.arnd@arndb.de> <20130426081646.GD24632@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Linus WALLEIJ , Arnd Bergmann , Linus Walleij , "linux-kernel@vger.kernel.org" , magnus.p.persson@stericsson.com, Herbert Xu , "linux-crypto@vger.kernel.org" , Andreas Westin , Lee Jones , "David S. Miller" , "linux-arm-kernel@lists.infradead.org" To: Vinod Koul Return-path: Content-Disposition: inline In-Reply-To: <20130426081646.GD24632@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org List-Id: linux-crypto.vger.kernel.org On Fri, Apr 26, 2013 at 01:46:46PM +0530, Vinod Koul wrote: > On Fri, Apr 26, 2013 at 10:28:39AM +0200, Linus Walleij wrote: > > On Thu, Apr 25, 2013 at 4:11 PM, Arnd Bergmann wrote: > > > > > The dma engine driver must know the address in its dma space, while the > > > slave driver has it available in physical space. These two are often the > > > same, but there is no generic way to convert between the two, especially > > > if the dma engine resides behind an IOMMU. > > > > > > The best assumption we can make is that the dma engine driver knows > > > how to convert between the two. Interestingly the documentation for > > > dma_slave_config talks about "physical address", while the structure > > > itself uses a dma_addr_t. Linus Walleij introduced the structure in > > > c156d0a5b0 "DMAENGINE: generic slave channel control v3", so I assume > > > he can shed some light on what he was thinking. I assume the documentation > > > is right but the structure is not and should be converted to use > > > phys_add_t or resource_size_t. > > > > OK I could cook a patch for that, but I think I need some input from > > Vinod and/or Russell on this. > the dma_slave_config is physical address that should be passed directly to the > controller. Obviosuly it should phys_addr_t :) What you've just said is actually confusing. "physical address" is normally the term used to describe the addresses seen to the RAM. phys_addr_t describes this. This is not necessarily what needs to be programmed into the DMA controller. For RAM addresses, they must be mapped via the DMA API - and this gives you a dma_addr_t. "DMA address" is the address to be programmed into a DMA controller to access a particular address in RAM or device, and has type dma_addr_t. When you're programming a DMA controller to access a device, you are clearly telling it the address on the _DMA controller's bus_ to access that register, which may or may not be the same as the physical address. There are platforms in existence where phys_addr_t can be 32-bit but dma_addr_t can be 64-bit. Getting this stuff wrong can cause problems.