Re: [PATCH] net: stmmac: xgmac: add missing parentheses to fix precendence error

[Colin Ian King]

On 02/10/2019 14:42, Dan Carpenter wrote:
> On Wed, Oct 02, 2019 at 04:33:57PM +0300, Dan Carpenter wrote:
>> On Wed, Oct 02, 2019 at 12:08:49PM +0100, Colin King wrote:
>>> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>>>
>>> The expression !(hw_cap & XGMAC_HWFEAT_RAVSEL) >> 10 is always zero, so
>>> the masking operation is incorrect. Fix this by adding the missing
>>> parentheses to correctly bind the negate operator on the entire expression.
>>>
>>> Addresses-Coverity: ("Operands don't affect result")
>>> Fixes: c2b69474d63b ("net: stmmac: xgmac: Correct RAVSEL field interpretation")
>>> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>>> ---
>>>  drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
>>> index 965cbe3e6f51..2e814aa64a5c 100644
>>> --- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
>>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
>>> @@ -369,7 +369,7 @@ static void dwxgmac2_get_hw_feature(void __iomem *ioaddr,
>>>  	dma_cap->eee = (hw_cap & XGMAC_HWFEAT_EEESEL) >> 13;
>>>  	dma_cap->atime_stamp = (hw_cap & XGMAC_HWFEAT_TSSEL) >> 12;
>>>  	dma_cap->av = (hw_cap & XGMAC_HWFEAT_AVSEL) >> 11;
>>> -	dma_cap->av &= !(hw_cap & XGMAC_HWFEAT_RAVSEL) >> 10;
>>> +	dma_cap->av &= !((hw_cap & XGMAC_HWFEAT_RAVSEL) >> 10);
>>
>> There is no point to the shift at all.
> 
> Sorry I meant to say it should be a bitwise NOT, right?  I was just
> looking at some other dma_cap stuff that did this same thing...  I can't
> find it now...

In drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c it is being used like
a boolean and not a bitmask'd value:

        if (!priv->dma_cap.av)

so the original logic is to do boolean flag merging rather than bit-wise
logic.

> 
> regards,
> dan carpenter
>