Re: [sur40] videobuf2 and/or DMA?

[David Herrmann <dh.herrmann@gmail.com>]

Hi

On Mon, Dec 8, 2014 at 8:50 AM, Florian Echtler <floe@butterbrot.org> wrote:
> Hello everyone,
>
> I'm preparing to finally add support for the raw sensor video stream to
> my driver for the SUR40 touchscreen. However, after an extensive amount
> of Googling, I'm still not clear on the relationship between DMA
> transfers, the USB core and the videobuf2 framework.
>
> Specifically, I'd like to know:
>
> - Can I always use DMA on the USB side (for bulk transfers), or does
> this in any way require support from the USB device's hardware? (I'm
> guessing no, but a definite answer would be great.)

I thought the USB API hides that from you? Nevertheless, this is a
question for linux-usb, not linux-input. I put some people on CC which
work on both, HID and USB. Maybe they can help you.

> - Regardless of the USB side of things, can I use the videobuf2
> framework without _having_ to use DMA? That way, I could get a basic
> driver running without DMA and switch later when it's convenient and/or
> the speedup is justified.

This is definitely a question for linux-media.

Thanks
David