netdev - Re: [net PATCH 1/2] net: dsa: qca8k: fix inband mgmt for big-endian systems

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Date:   Wed, 12 Oct 2022 14:42:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Christian Marangi <ansuelsmth@...il.com>
Cc:     Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pawel Dembicki <paweldembicki@...il.com>,
        Lech Perczak <lech.perczak@...il.com>
Subject: Re: [net PATCH 1/2] net: dsa: qca8k: fix inband mgmt for big-endian
 systems

On Mon, Oct 10, 2022 at 01:14:58PM +0200, Christian Marangi wrote:
> The header and the data of the skb for the inband mgmt requires
> to be in little-endian. This is problematic for big-endian system
> as the mgmt header is written in the cpu byte order.
> 
> Fix this by converting each value for the mgmt header and data to
> little-endian, and convert to cpu byte order the mgmt header and
> data sent by the switch.
> 
> Fixes: 5950c7c0a68c ("net: dsa: qca8k: add support for mgmt read/write in Ethernet packet")
> Tested-by: Pawel Dembicki <paweldembicki@...il.com>
> Tested-by: Lech Perczak <lech.perczak@...il.com>
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> Reviewed-by: Lech Perczak <lech.perczak@...il.com>
> ---
>  drivers/net/dsa/qca/qca8k-8xxx.c | 63 ++++++++++++++++++++++++--------
>  include/linux/dsa/tag_qca.h      |  6 +--
>  2 files changed, 50 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
> index 5669c92c93f7..4bb9b7eac68b 100644
> --- a/drivers/net/dsa/qca/qca8k-8xxx.c
> +++ b/drivers/net/dsa/qca/qca8k-8xxx.c
> @@ -137,27 +137,42 @@ static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
>  	struct qca8k_mgmt_eth_data *mgmt_eth_data;
>  	struct qca8k_priv *priv = ds->priv;
>  	struct qca_mgmt_ethhdr *mgmt_ethhdr;
> +	u32 command;
>  	u8 len, cmd;
> +	int i;
>  
>  	mgmt_ethhdr = (struct qca_mgmt_ethhdr *)skb_mac_header(skb);
>  	mgmt_eth_data = &priv->mgmt_eth_data;
>  
> -	cmd = FIELD_GET(QCA_HDR_MGMT_CMD, mgmt_ethhdr->command);
> -	len = FIELD_GET(QCA_HDR_MGMT_LENGTH, mgmt_ethhdr->command);
> +	command = le32_to_cpu(mgmt_ethhdr->command);
> +	cmd = FIELD_GET(QCA_HDR_MGMT_CMD, command);
> +	len = FIELD_GET(QCA_HDR_MGMT_LENGTH, command);

Humm...

This might have the same alignment issue as the second patch. In fact,
because the Ethernet header is 14 bytes in size, it is often
deliberately out of alignment by 2 bytes, so that the IP header is
aligned. You should probably be using get_unaligned_le32() when
accessing members of mgmt_ethhdr.

	  Andrew