From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Wed, 07 Sep 2016 10:29:25 +0200 Subject: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev In-Reply-To: <340685cd-7f06-21db-94cb-a87d0df36286@ti.com> References: <5147808.apZTAZ3VPE@wuerfel> <340685cd-7f06-21db-94cb-a87d0df36286@ti.com> Message-ID: <8802454.xFheq55hVP@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wednesday, September 7, 2016 10:17:31 AM CEST Roger Quadros wrote: > > > > Speaking of that flag, I suppose we need the same logic to know where > > to look for USB devices attached to a dwc3 host when we need to describe > > them in DT. By default we look for child device nodes under the > > node of the HCD device node, but that would be wrong here too. > > I didn't get this part. Information about USB devices attached to a USB host > is never provided in DT because they are always dynamically created via > usb_new_device(), whether they are hard-wired on the board or hot-plugged. > > These USB devices inherit their DMA masks in the usb_alloc_dev() routine > whereas each interface within the USB device inherits its DMA mask in > usb_set_configuration(). We had talked about adding support for this for at least six years (probably much more), but Peter Chen finally added it this year in commit 69bec72598 ("USB: core: let USB device know device node"). The main use for it is to let you specify a MAC address for on-board ethernet devices that lack an EPROM, but any other information can be added that way too. > There is a bug in the USB core because of which the ISB device and interfaces > do not inherit dma_pfn_offset correctly for which I've sent a patch > https://lkml.org/lkml/2016/8/17/275 I'm a bit skeptical about this. Clearly if we set the dma_mask, we should also set the dma_pfn_offset, but what exactly is this used for in USB devices? As I understand it, the dma_mask/dma_pfn_offset etc is used for the DMA mapping interface, but that can't really be used on USB devices, which I assume use usb_alloc_coherent() and the URB interfaces for passing data between a USB driver and the HCD. My knowledge of USB device drivers is a bit lacking, so it's possible I'm misunderstanding things here. Arnd