netdev - Re: [PATCH v3 4/4] USBNET: ax88179_178a: enable tso if usb host supports sg dma

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Date:	Thu, 8 Aug 2013 10:25:37 -0700
From:	Grant Grundler <grundler@...gle.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Oliver Neukum <oneukum@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	netdev <netdev@...r.kernel.org>, linux-usb@...r.kernel.org,
	Ben Hutchings <bhutchings@...arflare.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Freddy Xin <freddy@...x.com.tw>
Subject: Re: [PATCH v3 4/4] USBNET: ax88179_178a: enable tso if usb host
 supports sg dma

On Tue, Aug 6, 2013 at 5:41 PM, Ming Lei <ming.lei@...onical.com> wrote:
> On Wed, Aug 7, 2013 at 1:09 AM, Grant Grundler <grundler@...gle.com> wrote:
...
>> Following that logic, shouldn't all the features/hw_features settings
>> be removed from reset code path?
>
> This patch won't touch other settings because that isn't related with
> this patch.

Sorry - I didn't mean to imply your patch should do this. I was hoping
for a yes/no answer from you, Eric, or Dave.

...
>> I'll note that any "hiccup" in the USB side that causes the device to
>> get dropped and re-probed will cause the same symptom. There is
>
> I am afraid that PCI network devices' setting still won't survive unbound&
> re-probed, will they?

Correct - but PCI isn't as prone to "dropping off the bus" like USB
is. Master aborts on some PCI systems is a "Fatal Exception" and AFAIK
that's never been true for any USB device.

>> nothing the driver can do about it in this case. Perhaps add some udev
>> rules to preserve ethtool settings the same way I've seen udev rules
>> to record MAC address to enumerate devices (eth0, eth1, etc.)
>
> Some usbnet devices may have random MAC address assigned in every
> probe().

Ugh - ok. Then those scripts are broken for those devices. C'est la Vie.

My point is the mechanism (udev) exists to preserve any settings
ethtool can read/record the state of.

cheers,
grant

ps. thanks again for posting the USBNET sg dma series - I will likely
back port those to our chromeos-3.8 tree in the near future.
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