Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756036Ab3HWP4b (ORCPT ); Fri, 23 Aug 2013 11:56:31 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:36911 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754132Ab3HWP42 (ORCPT ); Fri, 23 Aug 2013 11:56:28 -0400 Message-ID: <52178628.5020702@wwwdotorg.org> Date: Fri, 23 Aug 2013 09:56:24 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130803 Thunderbird/17.0.8 MIME-Version: 1.0 To: Richard Zhao CC: "linux-kernel@vger.kernel.org" , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "vinod.koul@intel.com" , "djbw@fb.com" , "grant.likely@linaro.org" , "rob.herring@calxeda.com" , "devicetree@vger.kernel.org" Subject: Re: [PATCH v2] DMA: add help function to check whether dma controller registered References: <1375423458-6868-1-git-send-email-rizhao@nvidia.com> <1377153781-18006-1-git-send-email-rizhao@nvidia.com> <52167665.90602@wwwdotorg.org> <20130823011738.GA17925@rizhao-lap> In-Reply-To: <20130823011738.GA17925@rizhao-lap> X-Enigmail-Version: 1.4.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1860 Lines: 44 On 08/22/2013 07:17 PM, Richard Zhao wrote: > On Fri, Aug 23, 2013 at 04:36:53AM +0800, Stephen Warren wrote: >> On 08/22/2013 12:43 AM, Richard Zhao wrote: >>> DMA client device driver usually needs to know at probe time whether >>> dma controller has been registered to deffer probe. So add a help >>> function of_dma_check_controller. >>> >>> DMA request channel functions can also used to check it, but they >>> are usually called at open() time. >> >> This new function is almost identical to the existing >> of_dma_request_slave_channel(). Surely the code should be shared? > > ofdma->of_dma_xlate(&dma_spec, ofdma); > The above is called holding of_dma_lock. If I want to abstract the > common lines, there' two options. What is the problem with acquiring the lock? If request_slave_channel() needs to take the lock, then there must be a reason which presumably applies to the other path too. ... >> But that said, I don't see any need for a new function; why can't >> drivers simply call of_dma_request_slave_channel() at probe time; > > It'll mislead user. channel supposed to be request at open time. I don't agree. >> from >> what I can see, that function doesn't actually request the channel, but >> rather simply looks it up, just like this one. The only difference is >> that of_dma_xlate() is also called, but that's just doing some data >> transformation, not actually recording channel ownership. > > xlate function request the channel if things go well. Oh. xlate should not do that; that's a design flaw. xlate should do nothing more than translate the DT content to an internal channel ID. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/