On Wed, 2013-09-18 at 17:52 +0200, Bjørn Mork wrote:
> No modern device should need the padding. No old device will be able to
> use the SG feature as implemented. You only enable it on USB3, don't
On XHCI.
> you? If this feature is restricted to USB3 capable devices, then it most
> certainly can be restricted to ZLP capable devices with absolutely no
> difference in the resulting set of supported devices.
No, USB 3.0 uses no companion controllers, so you can have devices
of any speed connected to it.
> Anyway, if you want to keep the padding for SG then maybe this will work
> and allow you to drop the extra struct usbnet field and allocation:
>
> if (skb_tailroom(skb) && !dev->can_dma_sg) {
> skb->data[skb->len] = 0;
> __skb_put(skb, 1);
> } else if (dev->can_dma_sg) {
> sg_set_buf(&urb->sg[urb->num_sgs++], skb->data, 1);
> }
>
> I.e. cheat and use the skb->data buffer twice, if that is allowed? The
> actual value of the padding byte should not matter, I believe?
That makes me immediately suspect a violation of the DMA rules.
Regards
Oliver
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