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

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Date:	Fri, 15 Jul 2016 15:41:10 -0700
From:	Bin Gao <bin.gao@...ux.intel.com>
To:	Felipe Balbi <felipe.balbi@...ux.intel.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	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

On Fri, Jul 15, 2016 at 02:21:48PM +0300, Felipe Balbi wrote:
> Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
> > On Fri, Jul 15, 2016 at 01:38:12PM +0300, Felipe Balbi wrote:
> >> 
> >> Hi,
> >> 
> >> Bin Gao <bin.gao@...ux.intel.com> writes:
> >> > +static void print_message(int port, bool is_cmsg, u8 msg, bool recv)
> >> > +{
> >> > +	pr_info("sink port %d: %s message %s %s\n", port,
> >> > +				is_cmsg ? "Control" : "Data",
> >> > +				msg_to_string(is_cmsg, msg),
> >> > +		 recv ? "received" : "sent(wait GOODCRC)");
> >> > +}
> >> 
> >> this is problematic. By default, we're all using 115200 8N1 baud
> >> rate. This message alone prints anywhere from 50 to 100 characters (I
> >> didn't really count properly, these are rough numbers), and that takes:
> >> 
> >> n50chars_time = 50 / (115200 / 10) = 4.3ms
> >> n100chars_time = 100 / (115200 / 10) = 8.6ms
> >> 
> >> Considering you have 30ms to reply with Power Request after GoodCRC, and
> >> considering you're printing several of these messages, they become
> >> really expensive and eat up valuable time from tSenderReply.
> >
> > printk() should be async, so it shouldn't be that big of a deal.
> 
> I can actually see this causing problems ;-) With this pr_info(),
> sometimes tSenderReply times out and Source gives a HardReset. Without
> pr_info(), type-c analyzer tells me we reply in less than 1ms.
> 
> > What is wrong is that this isn't using dev_info().
> 
> right, that too.
> 
> -- 
> balbi

When we don't have a struct device pointer for this driver,
a dev_info(NULL, fmt, ...) is equivalent to pr_info(). So we have to
use dev_info() here?
But I agree at least it should be pr_debug().