netdev - Re: [PATCH v3 -next 4/4] net: emaclite: Fix restricted cast warning of sparse

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Date:   Fri, 31 Jan 2020 14:48:49 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, anirudha.sarangi@...inx.com,
        michal.simek@...inx.com, gregkh@...uxfoundation.org,
        mchehab+samsung@...nel.org, john.linn@...inx.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 -next 4/4] net: emaclite: Fix restricted cast warning
 of sparse

On Fri, Jan 31, 2020 at 05:17:50PM +0530, Radhey Shyam Pandey wrote:
> Explicitly cast xemaclite_readl return value when it's passed to ntohl.
> Fixes below reported sparse warnings:
> 
> xilinx_emaclite.c:411:24: sparse: sparse: cast to restricted __be32
> xilinx_emaclite.c:420:36: sparse: sparse: cast to restricted __be32
> 
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
> Reported-by: kbuild test robot <lkp@...el.com>
> ---
>  drivers/net/ethernet/xilinx/xilinx_emaclite.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_emaclite.c b/drivers/net/ethernet/xilinx/xilinx_emaclite.c
> index 96e9d21..3273d4f 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_emaclite.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_emaclite.c
> @@ -408,7 +408,8 @@ static u16 xemaclite_recv_data(struct net_local *drvdata, u8 *data, int maxlen)
>  
>  	/* Get the protocol type of the ethernet frame that arrived
>  	 */
> -	proto_type = ((ntohl(xemaclite_readl(addr + XEL_HEADER_OFFSET +
> +	proto_type = ((ntohl((__force __be32)xemaclite_readl(addr +
> +			XEL_HEADER_OFFSET +
>  			XEL_RXBUFF_OFFSET)) >> XEL_HEADER_SHIFT) &
>  			XEL_RPLR_LENGTH_MASK);
>  
> @@ -417,7 +418,7 @@ static u16 xemaclite_recv_data(struct net_local *drvdata, u8 *data, int maxlen)
>  	 */
>  	if (proto_type > ETH_DATA_LEN) {
>  		if (proto_type == ETH_P_IP) {
> -			length = ((ntohl(xemaclite_readl(addr +
> +			length = ((ntohl((__force __be32)xemaclite_readl(addr +
>  					XEL_HEADER_IP_LENGTH_OFFSET +
>  					XEL_RXBUFF_OFFSET)) >>
>  					XEL_HEADER_SHIFT) &

If i understand this code correctly, you need the ntohl because you
are poking around inside the packet. All the other uses of
xemaclite_readl() are for descriptors etc.

It would be cleaner if you defined a xemaclite_readlbe32. If you use
ioread32be() it will do the endinness swap for you, so you don't need
the ntohl() and the horrible cast.

    Andrew