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

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Message-ID: <31258833-174f-080b-489e-85d3556bd1de@canonical.com>
Date:   Thu, 22 Aug 2019 17:11:19 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Larry Finger <Larry.Finger@...inger.net>,
        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 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.

> 
> Larry