From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756708Ab2CHLWM (ORCPT ); Thu, 8 Mar 2012 06:22:12 -0500 Received: from moutng.kundenserver.de ([212.227.126.171]:63821 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752089Ab2CHLWE (ORCPT ); Thu, 8 Mar 2012 06:22:04 -0500 Date: Thu, 8 Mar 2012 12:22:00 +0100 (CET) From: Guennadi Liakhovetski X-X-Sender: lyakh@axis700.grange To: Vinod Koul cc: Russell King - ARM Linux , linux-kernel@vger.kernel.org, "'Jassi Brar'" , Linus Walleij , Magnus Damm , Paul Mundt Subject: Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel() In-Reply-To: <1331204128.4657.54.camel@vkoul-udesk3> Message-ID: References: <1331101687.24656.319.camel@vkoul-udesk3> <20120307093026.GM17370@n2100.arm.linux.org.uk> <20120307103112.GP17370@n2100.arm.linux.org.uk> <20120307124620.GT17370@n2100.arm.linux.org.uk> <20120307142634.GA18787@n2100.arm.linux.org.uk> <20120307162755.GB18787@n2100.arm.linux.org.uk> <1331188201.4657.51.camel@vkoul-udesk3> <1331204128.4657.54.camel@vkoul-udesk3> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Provags-ID: V02:K0:o9hmeHIcejlvBTsch9/e+uj7aw19/Ig8/UA/o5dNgcJ cc/bjKgHLqS9RWeCuN+oIrCnr3g/nCnM5OcqqAIk/xJ7nRPrxf b7BVRCCtFysUClW3qEw2OGVoI7MbL0K7QAJBTrsLycxZq14sOZ N3xST3cQCdqN6aSvxx6MUghnR6ZDNIXZkVKOLL+LktMCwtzHo9 s+QH0Y2KSzLFRc37K9ZRg4KKmLKFTl3Y8hU3WiUAZaHedXAla9 62t8f8skYWcR7hxz93plxMW7ywgWDFQLGLIbeUOAmgQGqrh9Zh 5EbxjTK3Uap2YngPxFNEuj+kn8i4nAf1RzlTEJRxttFLH3LlwS 9nNmVkddeArOB13g5p4OkHnU0yFBj0fO7ehv3eS6KRIUVfs7CW LBfBGyq5vOhdQ== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 8 Mar 2012, Vinod Koul wrote: > On Thu, 2012-03-08 at 11:16 +0100, Guennadi Liakhovetski wrote: > > I still have the impression, that my specific use-case (sh-mobile), where > > channels can be freely configured for use by _ANY_ client on one of > > _SEVERAL_ DMAC instances, is not fully understood or taken into account. > > For this driver any kind of fixed mapping means, that we'd have to use > > both virtual channels and controllers, adding _a lot_ of complexity to the > > DMAC driver and making the dmaengine core just an "obfuscation layer." > > Yes, I remember Russell proposing core helpers for this. They would help, > > but (1) when would they be available, (2) how well would they be suitable > > for us, (3) they'd take the coding / maintainance burden away, but > > wouldn't reduce complexity and run-time overhead. > Lets try to address you case as well. > On a typical platform Let's take the mackerel board with the sh7372 SoC. it's not the state of the art, but that's what I'm currently working with and it should give us a good enough idea > 1) how many dma controllers you have? currently supported 5 of 3 types (3 of type A, 1 of each of the types B and C), all handled by the same driver > 2) how many clients you have huh... many. Maybe like 20 or more, and more, that are not yet supported, using type A, and 1 for each of types B and C > 3) which client can use what controller channel? How is mapping decided, > do you have a mux, is it hard wired by soc designers,....? In general - with all the current sh-mobile hardware, that I'm aware of - there can be several controller instances on an SoC of each controller type. Inside each type all instances and all channels are freely configurable. So, of 20 Type A clients they can use any channels on any one of the 3 type A controllers. Types B and C are "degenerate" cases, there clients are practically hard-wired to a specific DMA controller. So, we don't have to decide on mappings for type A. We just pick up any free channels on any controller and configure them accordingly. Whether there's a mux somewhere - you can say so, but it's all inside the SoC, and it's configured automatically ones you configure a physical channel to serve a specific client. > Can you pls give a description so that we ensure all models fit in the > final solution? That's what I've been trying to do since several days now... I've been saying "multiple controllers with multiple channels all freely configurable for any device from a list" again and again... Seems I'm speaking some strange language, that noone understands. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/