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

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Message-ID: <554B678B.7090103@cogentembedded.com>
Date:	Thu, 07 May 2015 16:24:27 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Ruslan Bilovol <ruslan.bilovol@...il.com>, oneukum@...e.de
CC:	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: usb: allow MTU that is a multiple of USB packet
 size

Hello.

On 5/7/2015 12:49 PM, 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.

> Signed-off-by: Ruslan Bilovol <ruslan.bilovol@...il.com>
> ---
>   drivers/net/usb/usbnet.c |    6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)

> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index 733f4fe..09dc848 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -382,9 +382,11 @@ int usbnet_change_mtu (struct net_device *net, int new_mtu)
>
>   	if (new_mtu <= 0)
>   		return -EINVAL;
> -	// no second zero-length packet read wanted after mtu-sized packets
> +	/* warn about second zero-length packet read after mtu-sized packets */
>   	if ((ll_mtu % dev->maxpacket) == 0)
> -		return -EDOM;
> +		netdev_warn(dev->net, "MTU %d is a multiple of USB wMaxPacketSize (%d),"
> +				" consider possible performance degradation\n",

    Please do not wrap the kernel messages, it impedes grepping for them. 
scripts/checkpatch.pl is aware of this rule.

WBR, Sergei

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