From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751834AbcFVKNr (ORCPT <rfc822;w@1wt.eu>);
	Wed, 22 Jun 2016 06:13:47 -0400
Received: from mx2.suse.de ([195.135.220.15]:36741 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751255AbcFVKNh (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 22 Jun 2016 06:13:37 -0400
Message-ID: <1466590137.12516.5.camel@suse.com>
Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class
From: Oliver Neukum <oneukum@suse.com>
To: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>,
        Rajaram R <rajaram.officemail@gmail.com>,
        Felipe Balbi <felipe.balbi@linux.intel.com>,
        Mathias Nyman <mathias.nyman@linux.intel.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Guenter Roeck <linux@roeck-us.net>, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org
Date: Wed, 22 Jun 2016 12:08:57 +0200
In-Reply-To: <20160622093156.GA19856@kuha.fi.intel.com>
References: <1463661894-22820-1-git-send-email-heikki.krogerus@linux.intel.com>
	 <1466514532.2091.5.camel@suse.com>
	 <20160621135845.GA10715@kuha.fi.intel.com>
	 <1466541785.2014.16.camel@suse.com>
	 <20160622093156.GA19856@kuha.fi.intel.com>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.12.11 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 2016-06-22 at 12:31 +0300, Heikki Krogerus wrote:

Hi,

> > Now correct me, if I am misreading the spec. I am sure the system
> > will boot unless it needs ridiculous amounts of power, but
> > will we see anything on the screen? As far as I can tell the spec
> > actually says that you cannot enter an alternate mode without having
> > established a power contract.
> > If we really leave entering modes up to user space, we have lost
> > printk before getting into the initrd at the earliest.
> 
> With these boards, you will not see anything on the screen that is
> attached to a Type-C connector until the OS has booted to the point
> where it has negotiated the power contract and entered a mode.
> 
> If the system has BIOS/FW/EC capable of negotiating the power contract
> and enter a mode, but where we still are expected to take over the
> whole TCPM in OS, I think the connection will be reset.

Think about a DP over type C display with a USB PD power brick on a
daisy chain.
If the host needs more than 15W or more than 5V, a reset is suicide.

And losing earlyprintk hurts a lot.
This means we need USB PD statically in the kernel. And a kernel
based policy that brings up all displays.

	Regards
		Oliver