NanoNote UDC DMA Issue

Bas Wijnen wijnen at debian.org
Sun Jun 23 17:34:28 EDT 2013


Hi,

On Sun, Jun 23, 2013 at 11:14:44PM +0200, richard -rw- weinberger wrote:
> USB Device does not have DMA support and is therefore very slow.
> Also the USB mass storage gadget seems to need DMA.

I've successfully implemented mass storage on Iris without DMA (I don't
have support for DMA in Iris yet).  I don't know if Linux requires it,
though.

> The Linux driver supports it, but it is disabled by default and if I enable
> DMA USB Devices does not work at all.
> 
> Now I'm wondering, is this a known issue?

It wasn't known to me, but that doesn't mean much.

> Is DMA for the UDC just broken in HW?

I would not expect this.  However, it is quite possible that the
implementation has a bug; the SoC's programmers manual is not always
easy to understand.

Thanks,
Bas



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