linux-kernel - Re: [RFC PATCH 2/3] net: sparx5: Add Sparx5 switchdev driver

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Date:   Sat, 28 Nov 2020 19:45:14 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Steen Hegelund <steen.hegelund@...rochip.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Microsemi List <microsemi@...ts.bootlin.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/3] net: sparx5: Add Sparx5 switchdev driver

> +/* Add a potentially wrapping 32 bit value to a 64 bit counter */
> +static inline void sparx5_update_counter(u64 *cnt, u32 val)
> +{
> +	if (val < (*cnt & U32_MAX))
> +		*cnt += (u64)1 << 32; /* value has wrapped */
> +
> +	*cnt = (*cnt & ~(u64)U32_MAX) + val;
> +}

I don't follow what this is doing. Could you give some examples?

> +static const char *const sparx5_stats_layout[] = {
> +	"rx_in_bytes",
> +	"rx_symbol_err",
> +	"rx_pause",
> +	"rx_unsup_opcode",

> +static void sparx5_update_port_stats(struct sparx5 *sparx5, int portno)
> +{
> +	struct sparx5_port *spx5_port = sparx5->ports[portno];
> +	bool high_speed_dev = sparx5_is_high_speed_device(&spx5_port->conf);

Reverse christmas tree. Which in this case, means you need to move the
assignment into the body of the code.

> +static void sparx5_get_sset_strings(struct net_device *ndev, u32 sset, u8 *data)
> +{
> +	struct sparx5_port *port = netdev_priv(ndev);
> +	struct sparx5  *sparx5 = port->sparx5;
> +	int idx;
> +
> +	if (sset != ETH_SS_STATS)
> +		return;
> +
> +	for (idx = 0; idx < sparx5->num_stats; idx++)
> +		memcpy(data + idx * ETH_GSTRING_LEN,
> +		       sparx5->stats_layout[idx], ETH_GSTRING_LEN);

You cannot use memcpy here, because the strings you have defined are
not ETH_GSTRING_LEN long. We once had a driver which happened to have
its strings at the end of a page. The memcpy would copy the string,
but keep going passed the end of string, over the page boundary, and
trigger a segmentation fault.

	Andrew