netdev - Re: [PATCH net-next 1/9] drivers: net: xgene: Protect indirect MAC access

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Date:   Wed, 26 Apr 2017 17:06:23 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Iyappan Subramanian <isubramanian@....com>, davem@...emloft.net,
        netdev@...r.kernel.org
Cc:     Quan Nguyen <qnguyen@....com>, patches@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next 1/9] drivers: net: xgene: Protect indirect MAC
 access

On 04/26/2017 04:38 PM, Iyappan Subramanian wrote:
> From: Quan Nguyen <qnguyen@....com>
> 
> This patch adds lock to protect indirect mac access sequence.
> 
> Signed-off-by: Quan Nguyen <qnguyen@....com>
> Signed-off-by: Iyappan Subramanian <isubramanian@....com>
> ---
>  drivers/net/ethernet/apm/xgene/xgene_enet_hw.c    | 2 ++
>  drivers/net/ethernet/apm/xgene/xgene_enet_main.c  | 1 +
>  drivers/net/ethernet/apm/xgene/xgene_enet_main.h  | 1 +
>  drivers/net/ethernet/apm/xgene/xgene_enet_sgmac.c | 7 ++++++-
>  drivers/net/ethernet/apm/xgene/xgene_enet_xgmac.c | 2 ++
>  5 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_hw.c b/drivers/net/ethernet/apm/xgene/xgene_enet_hw.c
> index 2a835e0..3697ba7 100644
> --- a/drivers/net/ethernet/apm/xgene/xgene_enet_hw.c
> +++ b/drivers/net/ethernet/apm/xgene/xgene_enet_hw.c
> @@ -365,9 +365,11 @@ static void xgene_enet_rd_mcx_mac(struct xgene_enet_pdata *pdata,
>  	cmd = pdata->mcx_mac_addr + MAC_COMMAND_REG_OFFSET;
>  	cmd_done = pdata->mcx_mac_addr + MAC_COMMAND_DONE_REG_OFFSET;
>  
> +	spin_lock(&pdata->mac_lock);
>  	if (!xgene_enet_rd_indirect(addr, rd, cmd, cmd_done, rd_addr, rd_data))
>  		netdev_err(pdata->ndev, "MCX mac read failed, addr: %04x\n",
>  			   rd_addr);
> +	spin_unlock(&pdata->mac_lock);

Why not fold the spinlock manipulation within xgenet_enet_rd_indirect()?
That way the caller does not have to know that acquiring the spinlock is
required and you avoid potential bugs in the future where you are
missing the spinlock on indirect accesses?
-- 
Florian