Am Sonntag, den 11.02.2018, 22:17 +0200 schrieb Ran Shalit:
> On Tue, Feb 6, 2018 at 8:55 AM, Felipe Balbi
> <felipe.ba...@linux.intel.com> wrote:
> > 
> > 
> > Hi,
> > 
> > Ran Shalit <ransha...@gmail.com> writes:
> > > 
> > > Hello,
> > > 
> > > I check code in:
> > > https://elixir.free-electrons.com/linux/v3.3/source/drivers/usb/gadget/f_mass_storage.c
> > > but I see no API usage of DMA, yet it is being mentioned as if it is used.
> > 
> > but it is used. It's just managed by the UDC driver (dwc3, musb,
> > chipidea, Renesas, etc)
> > 
> Just to be sure,
> can I assume that other usb gadget drivers are using DMA (including
> gadgetfs for userspace driver) ?
> And it is also correct for host drivers  (such as camera device ) ?

None of these drivers are for hardware. They implement a protocol.
On the host as well as on the gadget side there are driver for the
actual host controllers (EHCI, XHCI, ...) as well as their gadget
equivalents.

Any of these drivers may or may not use DMA. Neither the assumption
that they use DMA or the assumption that they do not use DMA
is valid. In fact they may mix it.
Your code must be ready to cope with either usage.

        HTH
                Oliver

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