From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v3 0/4] PCI: get DMA configuration from parent device Date: Thu, 08 Jan 2015 23:27:14 +0100 Message-ID: <2785994.gTZ9chGdKf@wuerfel> References: <1420656594-8908-1-git-send-email-m-karicheri2@ti.com> <54ADBB89.8070503@ti.com> <1934001.D0JfDRp1gF@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <1934001.D0JfDRp1gF@wuerfel> Sender: linux-kernel-owner@vger.kernel.org To: Murali Karicheri Cc: bhelgaas@google.com, linux-arm-kernel@lists.infradead.org, joro@8bytes.org, grant.likely@linaro.org, robh+dt@kernel.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-pci@vger.kernel.org, will.deacon@arm.com, linux@arm.linux.org.uk List-Id: devicetree@vger.kernel.org On Thursday 08 January 2015 09:56:39 Arnd Bergmann wrote: > There is another interesting case, which is a USB host controller or > something similar behind a PCI bus. These are quite common and also > need to be handled in some form. Let's do just PCI first for now, but > be aware that this will come next. Should we assume that the ID that > is required for a device is either known from the device node, or > that it comes from a PCI device? That means for the USB case, we will > likely need to have some custom logic. There seems to be an implicit > assumption all over the kernel that all devices have the same IOMMU > instance, but we can't really rely on that here. > Update: I've checked the USB implementation and we are lucky because these interactions are all done by the USB host controller, and a USB device is not itself DMA capable. We don't have to do anything for USB. Arnd