From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030581Ab2CFNDp (ORCPT ); Tue, 6 Mar 2012 08:03:45 -0500 Received: from moutng.kundenserver.de ([212.227.17.9]:50990 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932142Ab2CFNDo (ORCPT ); Tue, 6 Mar 2012 08:03:44 -0500 Date: Tue, 6 Mar 2012 14:03:36 +0100 (CET) From: Guennadi Liakhovetski X-X-Sender: lyakh@axis700.grange To: Vinod Koul cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel() In-Reply-To: <1331035739.24656.201.camel@vkoul-udesk3> Message-ID: References: <1331022623.24656.191.camel@vkoul-udesk3> <1331035739.24656.201.camel@vkoul-udesk3> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Provags-ID: V02:K0:ndEzA8H3NqAhKYv9PdpArJM47YBGuftIV7Rg76CIFsL rW8mQtacyBkOkXGkNXx2bYq/1e48Wr/eJiP9gTr2Dy1csJUGyw YxmyiGoZGQuFBaU43QP6zOkJnNYrMVSx9zpcEf4JQIDhJYeoky narjaXCMjXcKjy4cONrRfrkCYZrtZqojBtEqKiWPDG+lGpvQqk hcqEx7Hy+9CAOE5GNwPT8GeuelJAOt+PQlt8n8yHsxVJlR8Igr aZAQJ16oVAzDqzwjrKsCyU12B7OpVHcIqZLmb55LzP6CQW8qJZ CI+osUTlPwUQpdk6EImjnU/cKR0BRl+VO6C9i/7HiMv0ShKRGh oJfi3PdcKPxTJnwIMK726e7hs1SQF4X2OdNEPVJu2aEODdwcVm 7nOy+uQX270Lw== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 6 Mar 2012, Vinod Koul wrote: > On Tue, 2012-03-06 at 09:53 +0100, Guennadi Liakhovetski wrote: > > Hi Vinod > > > > Thanks for your review. > > > > On Tue, 6 Mar 2012, Vinod Koul wrote: > > > > > On Fri, 2012-03-02 at 14:21 +0100, Guennadi Liakhovetski wrote: > > > > Hi Vinod > > > > > > > > On Wed, 1 Feb 2012, Guennadi Liakhovetski wrote: > > > sorry I thought I had replied, but looks like it got missed! > > > > > > > > > When performing slame DMA some dmaengine drivers need additional data from > > > typo ^^^^^^^^^ > > > > > client drivers to find out, whether they can support that specific client > > > > > and to configure the DMA channel for it. This additional data has to be > > > > > supplied by client drivers during channel allocation, i.e., with the > > > > > __dma_request_channel() function. This patch adds a new > > > > > struct dma_slave_desc with some basic data in it, further this struct can > > > > > be embedded in hardware-specific types to supply any auxiliary > > > > > configuration. > > > counter arguing shouldn't the client drivers find out of the channel > > > requested is capable or not, that can be alternate approach as well. > > > That way people implement this in the filer functions and find if this > > > is the channel we need rather than dmac finding out if it can service > > > the client or not. > > > > How shall clients find this out? This is system- and DMAC-specific, this > > has nothing to do with the client functionality. The proposed approach is: > > > > * a client driver (MMC, USB, anything else) is capable to use DMA uses the > > standard dmaengine API to transfer the data > > > > * if the platform, where it's running, is supplying any auxiliary data, > > that it has to pass to the DMAC driver, it can do so, without getting > > involved in the details, just passing a pointer > > > > * the most natural location to do this is IMHO when requesting a DMA > > channel > and in that case why do you need the new parameters to be passed back in > filter function. What is the role of filter in this case ? Sorry, who said I needed them? No changes are required to the filter function. As for its role - don't know, I didn't design it:-) In my case the filter will essentially become a "return true" dummy, respectively, it can simply be omitted. In general, I can hardly imagine a situation, where, say, an MMC driver would have internal knowledge about DMA channels on the system, allowing it to select a suitable one... So, I'm really not sure what it is for. Good, that it is at least optional. Maybe it can be deprecated with time. > > Now, on sh-mobile platforms you can realistically have around 5 DMAC > > instances with 2 or 6 channels each, of which, say, 3 controllers are > > suitable for MMC and 2 are not. How shall the filter function find this > > out? Call some ugly platform callback? Traverse some platform-specific > > lists? Or use a fixed channel, thus significantly reducing flexibility? > > Sorry, none of these options seems very attractive to me. > well you can counter argue that dmac does not have this information > either. But the DMAC is certainly a better match for making channel-selection decisions. > Bigger question is who knows about this mapping and how do we > incorporate this mapping into channel allocation The platform does. And this knowledge has to be passed to the relevant driver. But I think it's the DMAC driver, that is relevant, not the client driver. The platform would supply information like DMAC #1 channel #1 (can be used for) device #1 device #2 ... channel #2 ... ... And I don't think, it would be reasonable to let every slave driver use this information. These lists can also be optimised for specific platforms. E.g., on some sh-mobile SoCs you have two DMAC types. One of them can serve devices from list A on any channel, the other one - from list B. So, all you have to do, is to reference either A or B from your DMAC platform data. Whereas doing a reverse mapping: for each (potential) DMA user reference a list of channels, that it can use - would be really clumsy. > > > Frankly I prefer former model, as that way dmacs will present channel > > > capabilities, and clients can use as they deem fit. > > > > > > > > > > Signed-off-by: Guennadi Liakhovetski Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/