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

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Message-ID: <d3c16158-ef89-f5ee-2f67-4357c70e8fe9@lwfinger.net>
Date:   Thu, 22 Aug 2019 11:03:59 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Colin 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 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.

Has this change been tested?

Larry