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

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Date:	Thu, 20 Aug 2009 16:25:13 +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:

>> 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 understand your suggestion - why status == 0? doesn't the patch
> below do what you want instead?

Because I think (didn't read the manual) that these (inverted) bits
represent specific errors. So I suggested inverting them, then treating
as separate error bits, it should be easier to read.

That's only a suggestion of course (unless someone sends me the/a card -
non-returnable "donations" only please - and I can work on it
personally).

IOW all (inverted) bits = 1 => all bits zero after inversion => no
errors. This changes functionality a bit, and would need to be checked.
Otherwise, you could test: if ((status & FrameOk) == 0) then looks_good().

> diff --git a/drivers/net/wan/dscc4.c b/drivers/net/wan/dscc4.c
> index 8face5d..88534b6 100644
> --- a/drivers/net/wan/dscc4.c
> +++ b/drivers/net/wan/dscc4.c
> @@ -663,12 +663,12 @@ 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++;
> -		else if (!(skb->data[pkt_len] | ~(FrameVfr | FrameRab)))
> +		else if ((skb->data[pkt_len] & (FrameVfr | FrameRab)) !=
> +				FrameVfr | FrameRab)
>  			dev->stats.rx_length_errors++;
> -		else
> -			dev->stats.rx_errors++;
> +		dev->stats.rx_errors++;
>  		dev_kfree_skb_irq(skb);
>  	}
>  refill:

Guess it would do.
-- 
Krzysztof Halasa
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