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

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Date: Tue, 17 Oct 2023 12:46:07 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Simon Horman <horms@...nel.org>, 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>, 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 Tue, 2023-10-17 at 10:24 +0200, Simon Horman wrote:
> 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.

It looks like 'list' is only touched on control path, so it's should
not critical.

Cheers,

Paolo