Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754264AbaKDPAv (ORCPT ); Tue, 4 Nov 2014 10:00:51 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:13149 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753881AbaKDPAq (ORCPT ); Tue, 4 Nov 2014 10:00:46 -0500 X-IronPort-AV: E=Sophos;i="5.07,313,1413244800"; d="scan'208";a="189316018" Date: Tue, 4 Nov 2014 15:00:18 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Grygorii Strashko CC: Stefano Stabellini , Will Deacon , "xen-devel@lists.xensource.com" , "Ian.Campbell@citrix.com" , "konrad.wilk@oracle.com" , Catalin Marinas , "linux-kernel@vger.kernel.org" , "david.vrabel@citrix.com" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v7 3/8] arm64: introduce is_device_dma_coherent In-Reply-To: <5458B9FC.3050309@ti.com> Message-ID: References: <1414422568-19103-3-git-send-email-stefano.stabellini@eu.citrix.com> <20141103105716.GC23162@arm.com> <5458B9FC.3050309@ti.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 4 Nov 2014, Grygorii Strashko wrote: > Hi Stefano, > > On 11/03/2014 01:10 PM, Stefano Stabellini wrote: > > On Mon, 3 Nov 2014, Will Deacon wrote: > >> On Mon, Nov 03, 2014 at 10:46:03AM +0000, Stefano Stabellini wrote: > >>> On Mon, 27 Oct 2014, Stefano Stabellini wrote: > >>>> Introduce a boolean flag and an accessor function to check whether a > >>>> device is dma_coherent. Set the flag from set_arch_dma_coherent_ops. > >>>> > >>>> Signed-off-by: Stefano Stabellini > >>>> Signed-off-by: Catalin Marinas > >>>> CC: will.deacon@arm.com > >>> > >>> Will, Catalin, > >>> are you OK with this patch? > >> > >> It would be nicer if the dma_coherent flag didn't have to be duplicated by > >> each architecture in dev_archdata. Is there any reason not to put it in the > >> core code? > > > > Yes, there is a reason for it: if I added a boolean dma_coherent flag in > > struct device as Catalin initially suggested, what would be the default > > for each architecture? Where would I set it for arch that don't use > > device tree? It is not easy. > > > > I thought it would be better to introduce is_device_dma_coherent only on > > the architectures where it certainly makes sense to have it. In fact I > > checked and arm and arm64 are the only architectures to define > > set_arch_dma_coherent_ops at the moment. At that point if > > is_device_dma_coherent becomes arch-specific, it makes sense to store > > the flag in dev_archdata instead of struct device. > > The proposition from Will looks reasonable for me too, because > there is "small" side-effect of adding such kind of properties to > arch-specific data or even to the core device structure. ;( > > There are some sub-systems in kernel which do not create their devices > from DT and instead some host device populates its children devices manually. > Now, I know at least two cases: > - usb: dwc3 core creates xhci device manually > - pci: adds its client devices > > In such, case DMA configuration have to be propagated from host to > child (in our case host device's got DMA configuration from DT), like: > dma_set_coherent_mask(&xhci->dev, dwc->dev->coherent_dma_mask); > > xhci->dev.parent = dwc->dev; > xhci->dev.dma_mask = dwc->dev->dma_mask; > xhci->dev.dma_parms = dwc->dev->dma_parms; > > So, once new DMA property is added it has to be propagated from > host to child device too. > > Recently, the new property dma_pfn_offset was introduced in struct device > and such kind of problem was observed on keystone 2: > - for usb case it was fixed using Platform Bus notifier (xhci - platform device) > - for pci - the work is in progress, because solution with PCI Bus notifier > was rejected https://lkml.org/lkml/2014/10/10/308. > > In general, if dma_coherent will belong to struct device then > such problems will be possible to fix directly in drivers/subsystems: > xhci->dev.dma_coherent = dwc->dev->dma_coherent; > > But, if it will be arch-specific data then it will be impossible to > set it without introducing proper and arch-specific setters/getters functions. > > Also, as an idea, we are thinking about introducing something like: > void dma_apply_parent_cfg(struct device *dev, struct device *parent) > which will ensure that all DMA configuration properly copied from > parent to children device. Now it should be (as minimum for ARM): > dma_mask > coherent_dma_mask > dma_parms > dma_pfn_offset > dev_archdata->dma_ops > [dma_coherent]? I understand your concern but the problem you have goes far beyond a simple dma_coherent flag: what about all the other dev_archdata fields? Aside from dma_ops, on some other architectures there might be other data structrures in dev_archdata that need to be properly initialized from the parent. Your idea of introducing something like dma_apply_parent_cfg is the only solid solution I can see. However I would consider naming it something more generic like init_dev_from_parent to handle other possible configurations (inside or outside dev_archdata) that might have to be initialized from information on the parent device. Regarding the dma_coherent flag, I still prefer this approach because introducing the dma_coherent flag in dev_archdata wouldn't make this issue any worse than already is, but would avoid other problems as mentioned in my previous reply. -- 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/