linux-kernel - RE: [PATCH v3 0/2] usb: Check for DMA capable buffer sanity

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Date:   Wed, 31 May 2017 11:04:36 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Wolfram Sang' <wsa@...-dreams.de>,
        Florian Fainelli <f.fainelli@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Peter Chen <peter.chen@....com>, Roger Quadros <rogerq@...com>,
        Alan Stern <stern@...land.harvard.edu>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Javier Martinez Canillas <javier@....samsung.com>,
        Baoyou Xie <baoyou.xie@...aro.org>,
        Sekhar Nori <nsekhar@...com>, William wu <wulf@...k-chips.com>,
        Arnd Bergmann <arnd@...db.de>,
        Chris Bainbridge <chris.bainbridge@...il.com>,
        Wolfram Sang <wsa-dev@...g-engineering.com>,
        Krzysztof Opasiak <k.opasiak@...sung.com>,
        Felix Hädicke <felixhaedicke@....de>,
        Colin Ian King <colin.king@...onical.com>,
        "open list:USB SUBSYSTEM" <linux-usb@...r.kernel.org>,
        "clemens@...isch.de" <clemens@...isch.de>,
        "maksim.salau@...il.com" <maksim.salau@...il.com>
Subject: RE: [PATCH v3 0/2] usb: Check for DMA capable buffer sanity

From: Wolfram Sang
> Sent: 28 May 2017 17:04
> 
> On Fri, May 05, 2017 at 02:08:31PM -0700, Florian Fainelli wrote:
> > On 04/25/2017 05:56 PM, Florian Fainelli wrote:
> > > Changes in v3:
> > >
> > > - added check in usb_gadget_map_request_by_dev (Felipe), new patch
> > > - improved commit message description (Clemens)
> > > - added additiona checks for urb->setup_packet (Alan)
> > >
> > > Changes in v2:
> > >
> > > - moved the check from usb_start_wait_urb() to usb_hcd_map_urb_for_dma()
> >
> > Is this version looking good now? Thanks!
> 
> So, it seems I am in a similar situation with the I2C subsystem right
> now. I need to check the message buffers if they are DMA capable.
> 
> Because you have basically the same checks in 3 different places, and I
> need something similar for I2C, I wondered about a generic place to put
> these checks. Especially since we want future improvements to these
> checks applied everywhere immediately. Here is a small diff on what I
> have now:
...
> +			} else if (!is_dma_capable_addr(urb->transfer_buffer)) {

For a generic function I'd pass the length as well.
It might be that buffers that don't cross page boundaries might be
deemed 'dma-able'.

Possibly more useful would be a variant of (IIRC) dma_map_for_device()
that will allocate a suitable bounce buffer for non-dma memory.
I think it can already do so for memory that is outside the address
range that the device can address (eg for a 32bit PCIe master in 64bit
system).

	David