[PATCH] WAN: bit and/or confusion

[PATCH] WAN: bit and/or confusion

[Roel Kluin]

Fix the tests that check whether Frame* bits are not set

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
// vi drivers/net/wan/dscc4.c +307
#define FrameVfr	0x80
#define FrameRdo        0x40
#define FrameCrc	0x20
#define FrameRab	0x10

diff --git a/drivers/net/wan/dscc4.c b/drivers/net/wan/dscc4.c
index 8face5d..dd3c64a 100644
--- a/drivers/net/wan/dscc4.c
+++ 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++;
-		else if (!(skb->data[pkt_len] | ~(FrameVfr | FrameRab)))
+		else if (!(skb->data[pkt_len] & ~(FrameVfr | FrameRab)))
 			dev->stats.rx_length_errors++;
 		else
 			dev->stats.rx_errors++;

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

[David Miller]

From: Roel Kluin <roel.kluin@gmail.com>
Date: Fri, 14 Aug 2009 14:51:46 +0200

> Fix the tests that check whether Frame* bits are not set
> 
> Signed-off-by: Roel Kluin <roel.kluin@gmail.com>

Applied.

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

[Andrew Morton]

On Fri, 14 Aug 2009 14:51:46 +0200
Roel Kluin <roel.kluin@gmail.com> wrote:

> Fix the tests that check whether Frame* bits are not set
> 
> Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
> ---
> // vi drivers/net/wan/dscc4.c +307
> #define FrameVfr	0x80
> #define FrameRdo        0x40
> #define FrameCrc	0x20
> #define FrameRab	0x10
> 
> diff --git a/drivers/net/wan/dscc4.c b/drivers/net/wan/dscc4.c
> index 8face5d..dd3c64a 100644
> --- a/drivers/net/wan/dscc4.c
> +++ 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++;

that's

	if (!(x & 0xffffffdf))

which seems peculiar.  Should it have been

	else if (skb->data[pkt_len] & FrameCrc)

or

	else if (!(skb->data[pkt_len] & FrameCrc))


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

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

[David Miller]

From: Andrew Morton <akpm@linux-foundation.org>
Date: Fri, 14 Aug 2009 16:36:44 -0700

> On Fri, 14 Aug 2009 14:51:46 +0200
> Roel Kluin <roel.kluin@gmail.com> wrote:
> 
>> @@ -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++;
> 
> that's
> 
> 	if (!(x & 0xffffffdf))
> 
> which seems peculiar.  Should it have been
> 
> 	else if (skb->data[pkt_len] & FrameCrc)
> 
> or
> 
> 	else if (!(skb->data[pkt_len] & FrameCrc))

Indeed, I can't tell which variant would be correct.

I'm reverting until someone with a datasheet for this chip speaks up
:-)

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

[Andrew Morton]

On Fri, 14 Aug 2009 16:41:23 -0700 (PDT)
David Miller <davem@davemloft.net> wrote:

> From: Andrew Morton <akpm@linux-foundation.org>
> Date: Fri, 14 Aug 2009 16:36:44 -0700
> 
> > On Fri, 14 Aug 2009 14:51:46 +0200
> > Roel Kluin <roel.kluin@gmail.com> wrote:
> > 
> >> @@ -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++;
> > 
> > that's
> > 
> > 	if (!(x & 0xffffffdf))
> > 
> > which seems peculiar.  Should it have been
> > 
> > 	else if (skb->data[pkt_len] & FrameCrc)
> > 
> > or
> > 
> > 	else if (!(skb->data[pkt_len] & FrameCrc))
> 
> Indeed, I can't tell which variant would be correct.
> 
> I'm reverting until someone with a datasheet for this chip speaks up
> :-)

http://www.datasheet.in/download.php?id=39415

Page 383 and 384 say that bit 5 (CRC) is zero if the rx frame contained
errors.


So we need

	else if (!(skb->data[pkt_len] & FrameCrc))

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


vfr is "valid frame".  0 is invalid.

rab is "receive message aborted".  The data sheet doesn't actually say
if the bit is active-high or active-low (grr).  

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

[Roel Kluin]

Fix the tests that check whether Frame* bits are not set

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
> we need
> 
> 	else if (!(skb->data[pkt_len] & FrameCrc))

> vfr is "valid frame".  0 is invalid.
> 
> rab is "receive message aborted".  The data sheet doesn't actually say
> if the bit is active-high or active-low (grr).  

Maybe someone could test this?

diff --git a/drivers/net/wan/dscc4.c b/drivers/net/wan/dscc4.c
index 8face5d..b686050 100644
--- a/drivers/net/wan/dscc4.c
+++ 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++;
-		else if (!(skb->data[pkt_len] | ~(FrameVfr | FrameRab)))
+		else if (!(skb->data[pkt_len] & (FrameVfr | FrameRab)))
 			dev->stats.rx_length_errors++;
 		else
 			dev->stats.rx_errors++;

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

[Francois Romieu]

Roel Kluin <roel.kluin@gmail.com> :
[...]
> Maybe someone could test this?

I may undust a pair of card and a split box but do not hold your breath.

-- 
Ueimor

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

[Krzysztof Halasa]

Roel Kluin <roel.kluin@gmail.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

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

[Roel Kluin]

Fix the tests that check whether Frame* bits are not set

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---

>> -		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)

Ok, Francois Romieu, could you test this?

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

Roel

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:

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

[Krzysztof Halasa]

Roel Kluin <roel.kluin@gmail.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

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

[David Miller]

From: Roel Kluin <roel.kluin@gmail.com>
Date: Thu, 20 Aug 2009 16:04:40 +0200

> Fix the tests that check whether Frame* bits are not set
> 
> Signed-off-by: Roel Kluin <roel.kluin@gmail.com>

Applied to net-next-2.6, thanks.