linux-kernel - Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 07 Sep 2016 10:29:25 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Roger Quadros <rogerq@...com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Alan Stern <stern@...land.harvard.edu>,
        Felipe Balbi <balbi@...nel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Stuart Yoder <stuart.yoder@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        lkml <linux-kernel@...r.kernel.org>,
        Scott Wood <oss@...error.net>,
        David Fisher <david.fisher1@...opsys.com>,
        "Thang Q. Nguyen" <tqnguyen@....com>, Leo Li <pku.leo@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

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