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

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Message-ID: <fe3e6a33692a07d15287800749b688e796c43f9a.camel@sipsolutions.net>
Date:   Thu, 22 Aug 2019 18:55:07 +0200
From:   Johannes Berg <johannes@...solutions.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 Thu, 2019-08-22 at 14:35 +0100, 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;

The same bug/issue is in bcma_pcie_mdio_write() btw.

It *seems* correct to me - otherwise the "address" parameter to the
function is entirely unused, which can't really be right.

There are only two code paths that ever get here:
 * bcma_pcicore_serdes_workaround
 * bcma_core_pci_power_save

The register at 0 is BCMA_CORE_PCI_CTL, which only has a few bits so
even bad values written there by accident might not hurt much ...

So it seems possible that it was just always broken.

johannes