linux-kernel - Re: [RFC PATCHv2] usb: USB Type-C Connector Class

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Date:	Mon, 08 Aug 2016 10:52:40 +0200
From:	Oliver Neukum <oneukum@...e.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Rajaram R <rajaram.officemail@...il.com>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Guenter Roeck <linux@...ck-us.net>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class

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