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Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class
From: Oliver Neukum <oneukum@suse.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>,
        Rajaram R <rajaram.officemail@gmail.com>,
        Felipe Balbi <felipe.balbi@linux.intel.com>,
        Heikki Krogerus <heikki.krogerus@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: Mon, 08 Aug 2016 10:52:40 +0200
In-Reply-To: <20160807213710.GA27135@amd>
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On Sun, 2016-08-07 at 23:37 +0200, Pavel Machek wrote:
> Hi!
> 
> > > 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.
> 
> Yes please.
> 
> Of course, even that will hurt, because I guess that means printk()
> after USB, and that means late in the boot process, but better late in
> kernel than in initrd.

i can confirm that in a laptop with a decent firmware a docking
station is switched into the mode that will make the display work.
In principle all is well if we can manage a handover.

	Regards
		Oliver