On 01/09/2012 04:31 PM, Felipe Balbi wrote:
On Mon, Jan 09, 2012 at 07:09:41AM -0800, Greg KH wrote:
On Mon, Jan 09, 2012 at 03:32:38PM +0100, Sebastian Andrzej Siewior wrote:
On 01/09/2012 03:23 PM, Matthew Wilcox wrote:
On Mon, Jan 09, 2012 at 01:55:02PM +0100, Sebastian Andrzej Siewior wrote:
Hi Sarah,
I've been looking into UAS support for hcds without support for sg.
I think that's fundamentally the wrong approach. Instead, HCDs should
be modified to add support for SGs. I posted a patch series that made
progress towards that goal a while back.
That is what Felipe and I decided for the gadget framework.
Alan / Greg, any comments from your side?
HGs should be supporting sg, why are they not?
MUSB, for instance, when you're using it's internal DMA engine, that
thing can't support SGs and it has so many buffer rules (alignments,
size, etc) that it's the most useless thing out there ;-)
Supporting SGs means simply to walk over the sg list yourself and setup
transfers based on it. For the HCDs which can do only one transfer at a
time there is no benefit in adding that support.
The difference is that for a sg list with 4 entries we require now 4
URBs for the unsupported case and only one for the supported case. If
we add sg support to those drivers we need only one URB but we need an
additional pointer or something to keep track of the current progress.
So we save some memory here, add some extra code and complexity and
have the same amount of interrupts in terms of "transfer completed".
Sebastian
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