[PATCH] net: dsa: mv88e6xxx: fix handling of upper half of STATS_TYPE_PORT

[PATCH] net: dsa: mv88e6xxx: fix handling of upper half of STATS_TYPE_PORT

[Rasmus Villemoes]

Currently, the upper half of a 4-byte STATS_TYPE_PORT statistic ends
up in bits 47:32 of the return value, instead of bits 31:16 as they
should.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
---
I also noticed that it's a bit inconsistent that we return U64_MAX if
there's a read error in STATS_TYPE_PORT, while
mv88e6xxx_g1_stats_read() returns 0 in case of a read error. In
practice, register reads probably never fail so it doesn't matter.

 drivers/net/dsa/mv88e6xxx/chip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 370434bdbdab..317553d2cb21 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -785,7 +785,7 @@ static uint64_t _mv88e6xxx_get_ethtool_stat(struct mv88e6xxx_chip *chip,
 			err = mv88e6xxx_port_read(chip, port, s->reg + 1, &reg);
 			if (err)
 				return U64_MAX;
-			high = reg;
+			low |= ((u32)reg) << 16;
 		}
 		break;
 	case STATS_TYPE_BANK1:
-- 
2.20.1

Re: [PATCH] net: dsa: mv88e6xxx: fix handling of upper half of STATS_TYPE_PORT

[Andrew Lunn]

On Tue, May 28, 2019 at 01:17:10PM +0000, Rasmus Villemoes wrote:
> Currently, the upper half of a 4-byte STATS_TYPE_PORT statistic ends
> up in bits 47:32 of the return value, instead of bits 31:16 as they
> should.
> 
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

Hi Rasmus

Please include a Fixes tag, to indicate where the problem was
introduced. In this case, i think it was:

Fixes: 6e46e2d821bb ("net: dsa: mv88e6xxx: Fix u64 statistics")

And set the Subject to [PATCH net] to indicate this should be applied
to the net tree.

> ---
> I also noticed that it's a bit inconsistent that we return U64_MAX if
> there's a read error in STATS_TYPE_PORT, while
> mv88e6xxx_g1_stats_read() returns 0 in case of a read error. In
> practice, register reads probably never fail so it doesn't matter.
> 
>  drivers/net/dsa/mv88e6xxx/chip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> index 370434bdbdab..317553d2cb21 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -785,7 +785,7 @@ static uint64_t _mv88e6xxx_get_ethtool_stat(struct mv88e6xxx_chip *chip,
>  			err = mv88e6xxx_port_read(chip, port, s->reg + 1, &reg);
>  			if (err)
>  				return U64_MAX;
> -			high = reg;
> +			low |= ((u32)reg) << 16;
>  		}
>  		break;
>  	case STATS_TYPE_BANK1:

What i don't like about this is how the function finishes:

       	}
        value = (((u64)high) << 32) | low;
        return value;
}

A better fix might be

-		break
+		value = (((u64)high) << 16 | low;
+		return value;

	Andrew	

Re: [PATCH] net: dsa: mv88e6xxx: fix handling of upper half of STATS_TYPE_PORT

[Rasmus Villemoes]

On 28/05/2019 15.44, Andrew Lunn wrote:
> On Tue, May 28, 2019 at 01:17:10PM +0000, Rasmus Villemoes wrote:
>> Currently, the upper half of a 4-byte STATS_TYPE_PORT statistic ends
>> up in bits 47:32 of the return value, instead of bits 31:16 as they
>> should.
>>
>> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
> 
> Hi Rasmus
> 
> Please include a Fixes tag, to indicate where the problem was
> introduced. In this case, i think it was:
> 
> Fixes: 6e46e2d821bb ("net: dsa: mv88e6xxx: Fix u64 statistics")
> 
> And set the Subject to [PATCH net] to indicate this should be applied
> to the net tree.

Will do.

>> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
>> index 370434bdbdab..317553d2cb21 100644
>> --- a/drivers/net/dsa/mv88e6xxx/chip.c
>> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
>> @@ -785,7 +785,7 @@ static uint64_t _mv88e6xxx_get_ethtool_stat(struct mv88e6xxx_chip *chip,
>>  			err = mv88e6xxx_port_read(chip, port, s->reg + 1, &reg);
>>  			if (err)
>>  				return U64_MAX;
>> -			high = reg;
>> +			low |= ((u32)reg) << 16;
>>  		}
>>  		break;
>>  	case STATS_TYPE_BANK1:
> 
> What i don't like about this is how the function finishes:
> 
>        	}
>         value = (((u64)high) << 32) | low;
>         return value;
> }
> 
> A better fix might be
> 
> -		break
> +		value = (((u64)high) << 16 | low;
> +		return value;

Why? It's odd to have the u32 "high" sometimes represent the high 32
bits, sometimes the third 16 bits. It would make it harder to support an
8-byte STATS_TYPE_PORT statistic. I think the code is much cleaner if
each case is just responsible for providing the upper/lower 32 bits,
then have the common case combine them; . It's just that in the
STATS_TYPE_BANK cases, the 32 bits are assembled from two 16 bit values
by a helper (mv88e6xxx_g1_stats_read), while it is "open-coded" in the
first case.

I'll resend my patch with the fixes tag (thanks for finding that; I had
already dug way too deep past that one) and fixed subject.

Rasmus


> 	Andrew	
> 


-- 
Rasmus Villemoes
Software Developer
Prevas A/S
Hedeager 3
DK-8200 Aarhus N
+45 51210274
rasmus.villemoes@prevas.dk
www.prevas.dk

Re: [PATCH] net: dsa: mv88e6xxx: fix handling of upper half of STATS_TYPE_PORT

[Vivien Didelot]

Hi Rasmus, Andrew,

On Wed, 29 May 2019 06:42:53 +0000, Rasmus Villemoes <rasmus.villemoes@prevas.dk> wrote:
> On 28/05/2019 15.44, Andrew Lunn wrote:
> > On Tue, May 28, 2019 at 01:17:10PM +0000, Rasmus Villemoes wrote:
> >> Currently, the upper half of a 4-byte STATS_TYPE_PORT statistic ends
> >> up in bits 47:32 of the return value, instead of bits 31:16 as they
> >> should.
> >>
> >> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
> > 
> > Hi Rasmus
> > 
> > Please include a Fixes tag, to indicate where the problem was
> > introduced. In this case, i think it was:
> > 
> > Fixes: 6e46e2d821bb ("net: dsa: mv88e6xxx: Fix u64 statistics")
> > 
> > And set the Subject to [PATCH net] to indicate this should be applied
> > to the net tree.
> 
> Will do.
> 
> >> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> >> index 370434bdbdab..317553d2cb21 100644
> >> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> >> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> >> @@ -785,7 +785,7 @@ static uint64_t _mv88e6xxx_get_ethtool_stat(struct mv88e6xxx_chip *chip,
> >>  			err = mv88e6xxx_port_read(chip, port, s->reg + 1, &reg);
> >>  			if (err)
> >>  				return U64_MAX;
> >> -			high = reg;
> >> +			low |= ((u32)reg) << 16;
> >>  		}
> >>  		break;
> >>  	case STATS_TYPE_BANK1:
> > 
> > What i don't like about this is how the function finishes:
> > 
> >        	}
> >         value = (((u64)high) << 32) | low;
> >         return value;
> > }
> > 
> > A better fix might be
> > 
> > -		break
> > +		value = (((u64)high) << 16 | low;
> > +		return value;
> 
> Why? It's odd to have the u32 "high" sometimes represent the high 32
> bits, sometimes the third 16 bits. It would make it harder to support an
> 8-byte STATS_TYPE_PORT statistic. I think the code is much cleaner if
> each case is just responsible for providing the upper/lower 32 bits,
> then have the common case combine them; . It's just that in the
> STATS_TYPE_BANK cases, the 32 bits are assembled from two 16 bit values
> by a helper (mv88e6xxx_g1_stats_read), while it is "open-coded" in the
> first case.

Here "low" and "high" are u32 and refer to the upper and lower halves
of the u64 returned value. For a 4-byte STATS_TYPE_PORT value, the
second read refers to the bits 31:16, thus belongs to (the upper half
of) the lower half of the 64-bit returned value, i.e. "low".

The current return value is correct, as well as your patch.


Thanks,
Vivien