linux-kernel - Re: [PATCH] net: usb: allow MTU that is a multiple of USB packet size

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Message-ID: <1430996857.30151.8.camel@suse.de>
Date:	Thu, 07 May 2015 13:07:37 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Ruslan Bilovol <ruslan.bilovol@...il.com>
Cc:	netdev <netdev@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: usb: allow MTU that is a multiple of USB packet
 size

On Thu, 2015-05-07 at 13:51 +0300, Ruslan Bilovol wrote:
> Hi Oliver,
> 
> On Thu, May 7, 2015 at 1:11 PM, Oliver Neukum <oneukum@...e.de> wrote:
> > On Thu, 2015-05-07 at 12:49 +0300, Ruslan Bilovol wrote:
> >> Current usbnet driver rejects setting MTU that is a multiple
> >> of USB endpoint's wMaxPacketSize size. However, it may only
> >> lead to possible performance degradation but is not so
> >> critical that its using should be prohibited. So allow it
> >> but also warn user about possible issue.
> >
> > We have reports about devices reacting badly to ZLPs.
> > Unless you have a compelling reasons for this change
> > I have to reject it.
> 
> What devices do you mean here: USB network adapters or USB host controllers?

The network adapters

> If it's just network adapters, then we can create some kind of quirk handling
> for them and do not disable this functionality just because some buggy device
> can't work with it.

No. They are too many.

> My device works fine with ZLPs so I want to use this particular MTU under Linux
> like I do it under other operation systems.

We can have a white list, but the general case is just too dangerous.

	Sorry
		Oliver


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