linux-kernel - Re: [PATCH 1/2] usb: typec: Add USB Power Delivery sink port support

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Message-ID: <877fcjh1ar.fsf@linux.intel.com>
Date:	Mon, 18 Jul 2016 10:07:24 +0300
From:	Felipe Balbi <felipe.balbi@...ux.intel.com>
To:	Bin Gao <bin.gao@...ux.intel.com>
Cc:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bin Gao <bin.gao@...el.com>,
	Chandra Sekhar Anagani <chandra.sekhar.anagani@...el.com>
Subject: Re: [PATCH 1/2] usb: typec: Add USB Power Delivery sink port support


Hi,

Bin Gao <bin.gao@...ux.intel.com> writes:
>> > +int pd_sink_queue_msg(struct pd_sink_msg *msg)
>> > +{
>> > +	unsigned long flags;
>> > +	struct pd_sink_port *port;
>> > +
>> > +	if (msg->port < 0 || msg->port >= MAX_NR_SINK_PORTS) {
>> > +		pr_err("Invalid port number\n");
>> > +		return -EINVAL;
>> > +	}
>> > +
>> > +	port = sink_ports[msg->port];
>> > +
>> > +	spin_lock_irqsave(&port->rx_lock, flags);
>> > +	list_add_tail(&msg->list, &port->rx_list);
>> > +	spin_unlock_irqrestore(&port->rx_lock, flags);
>> > +
>> > +	queue_work(port->rx_wq, &port->rx_work);
>> 
>> can we really queue several messages at a time? It seems unfeasible to
>> me. It's not like we can queue several power request in a role. Why do
>> you need this workqueue? Why don't you process message here, in place?
> Some Type-C chargers send two messages in a short duration(less than 1 ms),
> e.g. a SOURCE_CAPABILITY follows the previous SOURCE_CAPABILITY, or a
> GET_SINK_CAPABILITY follows a previous SOURCE_CAPABILITY, etc. Queuing
> message to PD stack by Type-C phy driver typically happens in a interrupt
> context. So in this case a nested interrupt may happen. Our whole PD
> stack while processing one message is not re-entrant so the nested
> interrupt would cause a problem.

keep interrupts masked for as long as necessary until your message is
processed.

-- 
balbi

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