linux-kernel - Re: [PATCH] bcma: fix incorrect update of BCMA_CORE_PCI_MDIO

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Date:   Thu, 22 Aug 2019 11:38:04 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Colin Ian King <colin.king@...onical.com>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Rafał Miłecki <zajec5@...il.com>,
        linux-wireless@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bcma: fix incorrect update of BCMA_CORE_PCI_MDIO_DATA

On 8/22/19 11:11 AM, Colin Ian King wrote:
> On 22/08/2019 17:03, Larry Finger wrote:
>> On 8/22/19 8:35 AM, Colin King wrote:
>>> From: Colin Ian King <colin.king@...onical.com>
>>>
>>> An earlier commit re-worked the setting of the bitmask and is now
>>> assigning v with some bit flags rather than bitwise or-ing them
>>> into v, consequently the earlier bit-settings of v are being lost.
>>> Fix this by replacing an assignment with the bitwise or instead.
>>>
>>> Addresses-Coverity: ("Unused value")
>>> Fixes: 2be25cac8402 ("bcma: add constants for PCI and use them")
>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>>> ---
>>>    drivers/bcma/driver_pci.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/bcma/driver_pci.c b/drivers/bcma/driver_pci.c
>>> index f499a469e66d..d219ee947c07 100644
>>> --- a/drivers/bcma/driver_pci.c
>>> +++ b/drivers/bcma/driver_pci.c
>>> @@ -78,7 +78,7 @@ static u16 bcma_pcie_mdio_read(struct bcma_drv_pci
>>> *pc, u16 device, u8 address)
>>>            v |= (address << BCMA_CORE_PCI_MDIODATA_REGADDR_SHF_OLD);
>>>        }
>>>    -    v = BCMA_CORE_PCI_MDIODATA_START;
>>> +    v |= BCMA_CORE_PCI_MDIODATA_START;
>>>        v |= BCMA_CORE_PCI_MDIODATA_READ;
>>>        v |= BCMA_CORE_PCI_MDIODATA_TA;
>>
>> I'm not sure the "Fixes" attribute is correct.
>>
>> The changes for this section in commit 2be25cac8402 are
>>
>> -       v = (1 << 30); /* Start of Transaction */
>> -       v |= (1 << 28); /* Write Transaction */
>> -       v |= (1 << 17); /* Turnaround */
>> -       v |= (0x1F << 18);
>> +       v = BCMA_CORE_PCI_MDIODATA_START;
>> +       v |= BCMA_CORE_PCI_MDIODATA_WRITE;
>> +       v |= (BCMA_CORE_PCI_MDIODATA_DEV_ADDR <<
>> +             BCMA_CORE_PCI_MDIODATA_DEVADDR_SHF);
>> +       v |= (BCMA_CORE_PCI_MDIODATA_BLK_ADDR <<
>> +             BCMA_CORE_PCI_MDIODATA_REGADDR_SHF);
>> +       v |= BCMA_CORE_PCI_MDIODATA_TA;
>>
>> Because the code has done quite a bit of work on v just above this
>> section, I agree that this is likely an error, but that error happened
>> in an earlier commit. Thus 2be25cac8402 did not introduce the error,
>> merely copied it.
> 
> Ugh, this goes back further. I didn't spot that. I'm less confident of
> what the correct settings should be now.
> 
>>
>> Has this change been tested?
> 
> Afraid not, I don't have the H/W.

I admit that I looked at this only because I found it hard to believe that the 
collective wisdom of the list would have missed the usage of "=" instead of 
"|=". At least that test was passed. :)

Larry