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

[Bin Gao]

On Mon, Jul 18, 2016 at 10:07:24AM +0300, Felipe Balbi wrote:
> 
> Hi,
> 
> Bin Gao <bin.gao@xxxxxxxxxxxxxxx> 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.

Yes, that's a right way to go. 
We'll have to document this because there might be other Type-C
PHY drivers(other than Intel Whiskey Cove PMIC) to use the PD stack.

> 
> -- 
> balbi