From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH 00/11] of: Fix DMA configuration for non-DT masters Date: Wed, 25 Sep 2019 16:09:12 +0100 Message-ID: References: <20190924181244.7159-1-nsaenzjulienne@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org To: Nicolas Saenz Julienne , Rob Herring Cc: devicetree@vger.kernel.org, Frank Rowand , "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" , linux-wireless , "linux-kernel@vger.kernel.org" , linux-arm-msm , "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" , etnaviv@lists.freedesktop.org, dri-devel , xen-devel@lists.xenproject.org, linux-tegra@vger.kernel.org, Linux Media Mailing List , linux-pci@vger.kernel.org, Matthias Brugger , Florian Fainelli , james.quinlan@broadcom.com, Stefan Wahren , Dan Williams List-Id: devicetree@vger.kernel.org On 25/09/2019 15:52, Nicolas Saenz Julienne wrote: > On Tue, 2019-09-24 at 16:59 -0500, Rob Herring wrote: >> On Tue, Sep 24, 2019 at 1:12 PM Nicolas Saenz Julienne >> wrote: >>> Hi All, >>> this series tries to address one of the issues blocking us from >>> upstreaming Broadcom's STB PCIe controller[1]. Namely, the fact that >>> devices not represented in DT which sit behind a PCI bus fail to get the >>> bus' DMA addressing constraints. >>> >>> This is due to the fact that of_dma_configure() assumes it's receiving a >>> DT node representing the device being configured, as opposed to the PCIe >>> bridge node we currently pass. This causes the code to directly jump >>> into PCI's parent node when checking for 'dma-ranges' and misses >>> whatever was set there. >>> >>> To address this I create a new API in OF - inspired from Robin Murphys >>> original proposal[2] - which accepts a bus DT node as it's input in >>> order to configure a device's DMA constraints. The changes go deep into >>> of/address.c's implementation, as a device being having a DT node >>> assumption was pretty strong. >>> >>> On top of this work, I also cleaned up of_dma_configure() removing its >>> redundant arguments and creating an alternative function for the special >>> cases >>> not applicable to either the above case or the default usage. >>> >>> IMO the resulting functions are more explicit. They will probably >>> surface some hacky usages that can be properly fixed as I show with the >>> DT fixes on the Layerscape platform. >>> >>> This was also tested on a Raspberry Pi 4 with a custom PCIe driver and >>> on a Seattle AMD board. >> >> Humm, I've been working on this issue too. Looks similar though yours >> has a lot more churn and there's some other bugs I've found. > > That's good news, and yes now that I see it, some stuff on my series is overly > complicated. Specially around of_translate_*(). > > On top of that, you removed in of_dma_get_range(): > > - /* > - * At least empty ranges has to be defined for parent node if > - * DMA is supported > - */ > - if (!ranges) > - break; > > Which I assumed was bound to the standard and makes things easier. > >> Can you test out this branch[1]. I don't have any h/w needing this, >> but wrote a unittest and tested with modified QEMU. > > I reviewed everything, I did find a minor issue, see the patch attached. WRT that patch, the original intent of "force_dma" was purely to consider a device DMA-capable regardless of the presence of "dma-ranges". Expecting of_dma_configure() to do anything for a non-OF device has always been bogus - magic paravirt devices which appear out of nowhere and expect to be treated as genuine DMA masters are a separate problem that we haven't really approached yet. Robin.