netdev - Re: [PATCH] WAN: bit and/or confusion

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Message-ID: <m3iqgovrsv.fsf@intrepid.localdomain>
Date:	Sat, 15 Aug 2009 20:46:24 +0200
From:	Krzysztof Halasa <khc@...waw.pl>
To:	Roel Kluin <roel.kluin@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, romieu@...zoreil.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] WAN: bit and/or confusion

Roel Kluin <roel.kluin@...il.com> writes:

> +++ b/drivers/net/wan/dscc4.c
> @@ -663,9 +663,9 @@ static inline void dscc4_rx_skb(struct dscc4_dev_priv *dpriv,
>  	} else {
>  		if (skb->data[pkt_len] & FrameRdo)
>  			dev->stats.rx_fifo_errors++;
> -		else if (!(skb->data[pkt_len] | ~FrameCrc))
> +		else if (!(skb->data[pkt_len] & FrameCrc))
>  			dev->stats.rx_crc_errors++;

This looks like a correct fix.

> -		else if (!(skb->data[pkt_len] | ~(FrameVfr | FrameRab)))
> +		else if (!(skb->data[pkt_len] & (FrameVfr | FrameRab)))
>  			dev->stats.rx_length_errors++;

This test requires both FrameVfr and FrameRab to be true (zero). Perhaps
it should be:

> +		else if ((skb->data[pkt_len] & (FrameVfr | FrameRab)) != FrameVfr | FrameRab)

>  		else
>  			dev->stats.rx_errors++;

rx_errors is incremented only on remaining errors. I think most drivers
increment rx_errors on all RX errors, and simultaneously rx_*_errors
when needed.


Perhaps something like the following should be better?

		u8 status = ~skb->data[pkt_len];

		if (status == 0)
			looks_good...;
		else {
			if (status & FrameRab)
				...
			if (status & FrameVfr)
				...
			etc.
			rx_errors++;
		}

I don't have the hardware and can't test (donations of such hw welcome).
-- 
Krzysztof Halasa
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