netdev - Re: [PATCH net-next v6 3/3] mctp i3c: MCTP I3C driver

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Date: Tue, 17 Oct 2023 10:24:27 +0200
From: Simon Horman <horms@...nel.org>
To: Matt Johnston <matt@...econstruct.com.au>
Cc: linux-i3c@...ts.infradead.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jeremy Kerr <jk@...econstruct.com.au>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, miquel.raynal@...tlin.com
Subject: Re: [PATCH net-next v6 3/3] mctp i3c: MCTP I3C driver

On Fri, Oct 13, 2023 at 12:06:25PM +0800, Matt Johnston wrote:
> Provides MCTP network transport over an I3C bus, as specified in
> DMTF DSP0233.
> 
> Each I3C bus (with "mctp-controller" devicetree property) gets an
> "mctpi3cX" net device created. I3C devices are reachable as remote
> endpoints through that net device. Link layer addressing uses the
> I3C PID as a fixed hardware address for neighbour table entries.
> 
> The driver matches I3C devices that have the MIPI assigned DCR 0xCC for
> MCTP.
> 
> Signed-off-by: Matt Johnston <matt@...econstruct.com.au>

Hi Matt,

one minor nit below, which you can take, leave, or leave for later
as far as I am concerned.

Overall the patch looks good to me and I see that Paolo's review of v5 has
has been addressed.

Reviewed-by: Simon Horman <horms@...nel.org>

> +/* List of mctp_i3c_busdev */
> +static LIST_HEAD(busdevs);
> +/* Protects busdevs, as well as mctp_i3c_bus.devs lists */
> +static DEFINE_MUTEX(busdevs_lock);
> +
> +struct mctp_i3c_bus {
> +	struct net_device *ndev;
> +
> +	struct task_struct *tx_thread;
> +	wait_queue_head_t tx_wq;
> +	/* tx_lock protects tx_skb and devs */
> +	spinlock_t tx_lock;
> +	/* Next skb to transmit */
> +	struct sk_buff *tx_skb;
> +	/* Scratch buffer for xmit */
> +	u8 tx_scratch[MCTP_I3C_MAXBUF];
> +
> +	/* Element of busdevs */
> +	struct list_head list;

I am unsure if it is important, but I observe that on x86_64
list spans a cacheline.

> +
> +	/* Provisioned ID of our controller */
> +	u64 pid;
> +
> +	struct i3c_bus *bus;
> +	/* Head of mctp_i3c_device.list. Protected by busdevs_lock */
> +	struct list_head devs;
> +};

...