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

[David Laight]

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