netdev - Re: [PATCHv3] drivers/net/usb: Add new driver ipheth

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Date:	Sun, 4 Apr 2010 09:24:43 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	"L. Alberto Giménez" <agimenez@...valve.es>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linville@...driver.com,
	j.dumon@...ion.com, steve.glendinning@...c.com,
	davem@...emloft.net, gregkh@...e.de, dgiagio@...il.com,
	dborca@...oo.com
Subject: Re: [PATCHv3] drivers/net/usb: Add new driver ipheth

Am Freitag, 2. April 2010 20:23:21 schrieb L. Alberto Giménez:
> On 03/31/2010 10:33 PM, Oliver Neukum wrote:
> > Am Mittwoch, 31. März 2010 21:42:07 schrieb L. Alberto Giménez:
> 
> Hi Oliver,
> 
> Just like with Ben's comments I still have a couple of doubts about your
> comments.
> 
> 
> >> +
> >> +static int ipheth_open(struct net_device *net)
> >> +{
> >> +	struct ipheth_device *dev = netdev_priv(net);
> >> +	struct usb_device *udev = dev->udev;
> >> +	int retval = 0;
> >> +
> >> +	usb_set_interface(udev, IPHETH_INTFNUM, IPHETH_ALT_INTFNUM);
> >> +	usb_clear_halt(udev, usb_rcvbulkpipe(udev, dev->bulk_in));
> >> +	usb_clear_halt(udev, usb_sndbulkpipe(udev, dev->bulk_out));
> > 
> > Is this really needed? If so, please add a comment.
> 
> I understand that usb_clear_halt is only needed when the device has
> transmitted data, and as it is "open" time, we can assume that no
> transmissions ere made, so we don't need to clear anything (aka: remove
> both lines), am I right?

Clearing a halt is necessary only when a device has stalled due to an
error condition. Unless the device is buggy and produces errors for
no good reason you don't need these lines.
 
> >> +
> >> +	retval = ipheth_carrier_set(dev);
> >> +	if (retval)
> >> +		goto error;
> >> +
> >> +	retval = ipheth_rx_submit(dev, GFP_KERNEL);
> >> +	if (retval)
> >> +		goto error;
> >> +
> >> +	schedule_delayed_work(&dev->carrier_work, IPHETH_CARRIER_CHECK_TIMEOUT);
> > 
> > Does it make sense to start rx while you have no carrier?
> 
> Well, I have no clue about this one. I think that upstream developers
> should take a look into this (Dario, Daniel, could you?) since I don't
> have the knowledge to decide what to do about it.
> 
> But I assume that as with the previous one, we have just opened the
> device and we aren't (yet) doing anything with it, so we shouldn't start rx?

Your code as is is correct, I just wondered whether it could be made more
efficient.

> >> +static void ipheth_disconnect(struct usb_interface *intf)
> >> +{
> >> +	struct ipheth_device *dev;
> >> +
> >> +	dev = usb_get_intfdata(intf);
> >> +	if (dev != NULL) {
> > 
> > is this check needed?
> 
> Does usb_get_infdata always return not NULL? I haven't found anything

It returns what you gave it with  usb_set_intfdata().

> about it (just manual pages for the function, but can't spot if it
> cannot return NULL). We disconnected the device, but I understand that
> the kernel still has the information and the allocated memory, so the
> cleanup code is still needed, isn't it?

It is definitely needed.

> >> +static struct usb_driver ipheth_driver = {
> >> +	.name =		"ipheth",
> >> +	.probe =	ipheth_probe,
> >> +	.disconnect =	ipheth_disconnect,
> >> +	.id_table =	ipheth_table,
> >> +	.supports_autosuspend = 0,
> > 
> > redundant
> 
> Why?

0 is the default.

	Regards
		Oliver
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