linux-kernel - Re: [ 22/52] asix: Fix tx transfer padding for full-speed USB

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Message-ID: <4FAC081D.5080202@teksavvy.com>
Date:	Thu, 10 May 2012 14:25:33 -0400
From:	Mark Lord <kernel@...savvy.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Ingo van Lil <inguin@....de>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [ 22/52] asix: Fix tx transfer padding for full-speed USB

On 12-05-10 01:31 PM, Greg KH wrote:
> 3.3-stable review patch.  If anyone has any objections, please let me know.
..
> From: Ingo van Lil <inguin@....de>
> [ Upstream commit 2a5809499e35b53a6044fd34e72b242688b7a862 ]
> 
> The asix.c USB Ethernet driver avoids ending a tx transfer with a zero-
> length packet by appending a four-byte padding to transfers whose length
> is a multiple of maxpacket. However, the hard-coded 512 byte maxpacket
> length is valid for high-speed USB only; full-speed USB uses 64 byte
> packets.
> 
> Signed-off-by: Ingo van Lil <inguin@....de>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/net/usb/asix.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/drivers/net/usb/asix.c
> +++ b/drivers/net/usb/asix.c
> @@ -403,7 +403,7 @@ static struct sk_buff *asix_tx_fixup(str
>  	u32 packet_len;
>  	u32 padbytes = 0xffff0000;
>  
> -	padlen = ((skb->len + 4) % 512) ? 0 : 4;
> +	padlen = ((skb->len + 4) & (dev->maxpacket - 1)) ? 0 : 4;
>  
>  	if ((!skb_cloned(skb)) &&
>  	    ((headroom + tailroom) >= (4 + padlen))) {
> @@ -425,7 +425,7 @@ static struct sk_buff *asix_tx_fixup(str
>  	cpu_to_le32s(&packet_len);
>  	skb_copy_to_linear_data(skb, &packet_len, sizeof(packet_len));
>  
> -	if ((skb->len % 512) == 0) {
> +	if (padlen) {
>  		cpu_to_le32s(&padbytes);
>  		memcpy(skb_tail_pointer(skb), &padbytes, sizeof(padbytes));
>  		skb_put(skb, sizeof(padbytes));
> 
> 

This patch changes behaviour even for high-speed USB.
Was this intentional, and why?

Thanks
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