Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934143AbcCNK4u (ORCPT ); Mon, 14 Mar 2016 06:56:50 -0400 Received: from mail-pf0-f170.google.com ([209.85.192.170]:33085 "EHLO mail-pf0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934109AbcCNK4g (ORCPT ); Mon, 14 Mar 2016 06:56:36 -0400 Date: Mon, 14 Mar 2016 18:51:08 +0800 From: Peter Chen To: Li Yang Cc: Bjorn Andersson , Peter Chen , Arnd Bergmann , Greg Kroah-Hartman , Rajesh Bhagat , "linux-usb@vger.kernel.org" , lkml , Srinivas Kandagatla , linux-arm-msm , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] usb: chipidea: Configure DMA properties and ops from DT Message-ID: <20160314105108.GB2131@shlinux2.ap.freescale.net> References: <1456119133-16114-1-git-send-email-bjorn.andersson@linaro.org> <56CADCE9.9090305@linaro.org> <20160222220750.GI21240@tuxbot> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2948 Lines: 66 On Wed, Mar 09, 2016 at 05:16:50PM -0600, Li Yang wrote: > On Tue, Mar 8, 2016 at 9:40 PM, Bjorn Andersson > wrote: > > On Tue, Mar 8, 2016 at 11:52 AM, Li Yang wrote: > >> On Wed, Mar 2, 2016 at 4:59 PM, Li Yang wrote: > >>> On Mon, Feb 22, 2016 at 4:07 PM, Bjorn Andersson > >>> wrote: > >>>> On Mon 22 Feb 02:03 PST 2016, Srinivas Kandagatla wrote: > >>>> > >>>>> > >>>>> > >>>>> On 22/02/16 05:32, Bjorn Andersson wrote: > >>>>> >On certain platforms (e.g. ARM64) the dma_ops needs to be explicitly set > >>>>> >to be able to do DMA allocations, so use the of_dma_configure() helper > >>>>> >to populate the dma properties and assign an appropriate dma_ops. > > [..] > >>>>> None of the drivers call of_dma_configure() explicitly, which makes me feel > >>>>> that we are doing something wrong. TBH, this should be handled in more > >>>>> generic way rather than driver like this having an explicit call to > >>>>> of_dma_configure(). > >>>>> > >>>> > >>>> I agree, trying to figure out if it should be inherited or something. > >>> > >>> I also agree. We need address it in a more generic way. I did a > >>> search for platform_device_add()/platform_device_register() in the > >>> kernel source code. I found a lot of them and many could be also > >>> doing DMA. Looks like it is still too early to assume every device is > >>> already getting dma_ops set through bus probe. Otherwise, many > >>> drivers are potentially broken by this assumption. > >> > >> Any further comment on this topic? I added the linux-arm mailing list > >> which was missing from previous discussion. > >> > > > > I had the chance to go through this with Arnd and the verdict is that > > devices not described in DT should not do DMA (or allocate buffers for > > doing DMA). > > > > So I believe the solution is to fall back on Peter's description; the > > chipidea driver is the core driver and the Qualcomm code should just > > be a platform layer. > > > > My suggestion is that we turn the chipidea core into a set of APIs > > that can called by the platform specific pieces. That way we will have > > the chipidea core be the device described in the DT. > > But like I said, this problem is not just existing for chipidea > driver. We already found that the dwc3 driver is also suffering from > the same issue. I don't know how many other drivers are impacted by > this change, but I suspect there will be some. A grep of > platform_device_add() in driver/ directory returns many possible > drivers to be impacted. As far as I know, the > drivers/net/ethernet/freescale/fman/mac.c is registering child > ethernet devices that definitely will do dma. If you want to do this > kind of rework to all these drivers, it will be a really big effort. > +1 Yes, I think this DMA things should be covered by driver core too. -- Best Regards, Peter Chen