netdev - Re: [PATCH net-next v3 2/2] usbnet: ipheth: add CDC NCM support

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Date: Thu, 01 Jun 2023 10:09:30 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Foster Snowhill <forst@....gy>, "David S. Miller" <davem@...emloft.net>,
  Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>
Cc: Georgi Valkov <gvalkov@...il.com>, Simon Horman
 <simon.horman@...igine.com>,  Jan Kiszka <jan.kiszka@...mens.com>,
 linux-usb@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 2/2] usbnet: ipheth: add CDC NCM support

On Wed, 2023-05-31 at 17:10 +0200, Foster Snowhill wrote:
> > 
> > > 	memcpy(dev->tx_buf, skb->data, skb->len);
> > > -	if (skb->len < IPHETH_BUF_SIZE)
> > > -		memset(dev->tx_buf + skb->len, 0, IPHETH_BUF_SIZE - skb->len);
> > > 
> > >  	usb_fill_bulk_urb(dev->tx_urb, udev,
> > >  			  usb_sndbulkpipe(udev, dev->bulk_out),
> > > -			  dev->tx_buf, IPHETH_BUF_SIZE,
> > > +			  dev->tx_buf, skb->len,
> > >  			  ipheth_sndbulk_callback,
> > >  			  dev);
> > >  	dev->tx_urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
> > 
> > This chunk looks unrelated from NCM support, and unconditionally
> > changes the established behaviour even with legacy mode, why?
> > 
> > Does that works even with old(er) devices?
> 
> I see Georgi Valkov said he tested v3 of the patch on older iOS devices
> and confirmed it working. I'll chat with him to get some USB traffic
> captures, to check what is macOS' behaviour with such devices (to make
> sure we behave the same way as the official driver). I also wanted to
> investigate a bit, when was NCM support even added to iOS.
> 
> Personally I remember testing this in legacy mode a while ago, before
> I implemented NCM. I will re-test it again in legacy mode in addition
> to Georgi's efforts.
> 
> From my side, I think it's reasonable to split this out into a separate
> patch, since it technically applies to the legacy mode as well, and
> doesn't (directly) relate to NCM support, as you pointed out.

I think that would be the best option, so we have a clear separation
between what is needed for NCM support and other improvements.

Thanks!

Paolo