[sur40] videobuf2 and/or DMA?

[sur40] videobuf2 and/or DMA?

[Florian Echtler]

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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.)

- 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.

Thanks & best regards, Florian
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SENT FROM MY DEC VT50 TERMINAL




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Re: [sur40] videobuf2 and/or DMA?

[David Herrmann]

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