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

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Message-ID: <20160807213710.GA27135@amd>
Date:	Sun, 7 Aug 2016 23:37:10 +0200
From:	Pavel Machek <pavel@....cz>
To:	Oliver Neukum <oneukum@...e.com>
Cc:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Rajaram R <rajaram.officemail@...il.com>,
	Felipe Balbi <felipe.balbi@...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

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.

(And yes, N900 has display pretty late in the bootprocess, and yes, it
is very annoying.)

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html