linux-kernel - Re: [PATCH v3 4/4] can: kvaser_usb: Add support for the Usbcan-II family

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Message-ID: <54AFE03D.5040509@pengutronix.de>
Date:	Fri, 09 Jan 2015 15:05:49 +0100
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>
CC:	Olivier Sobrie <olivier@...rie.be>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Linux-CAN <linux-can@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/4] can: kvaser_usb: Add support for the Usbcan-II
 family

On 01/09/2015 04:06 AM, Ahmed S. Darwish wrote:
>>>
>>> 		cf->can_id |= CAN_ERR_CRTL;
>>> 		cf->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
>>>
>>> 		stats->rx_over_errors++;
>>> 		stats->rx_errors++;
>>>
>>> 		netif_rx(skb);
>>>
>>> 		stats->rx_packets++;
>>> 		stats->rx_bytes += cf->can_dlc;
>>
>> Another patch would be not to touch cf after netif_rx(), please
>> move the stats handling before calling netif_rx(). Same applies to
>> the kvaser_usb_rx_can_msg() function.

> BTW, is it guaranteed from the SocketCAN stack that netif_rx()

netif_rx() is the generic networking stack already.

> will never return NET_RX_DROPPED? Because if no guarantee
> exists, I guess below fragment cannot be completely correct?

No, it's not guaranteed...

> 
>         stats->rx_packets++;
>         stats->rx_bytes += cf->can_dlc;
>         netif_rx(skb);
> 
> On the other hand, I don't see evan a single CAN driver checking
> netif_rx() return value, so maybe such a check is an overkill...

A quick look shows that almost no ethernet or wireless drivers take care
about the return value. In case of a RX_DROPPED some increase a drop
counter, though.

Marc

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