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

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Message-ID: <87k2gngn8z.fsf@linux.intel.com>
Date:	Fri, 15 Jul 2016 14:21:48 +0300
From:	Felipe Balbi <felipe.balbi@...ux.intel.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Bin Gao <bin.gao@...ux.intel.com>,
	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


Hi,

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

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