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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1466541785.2014.16.camel@suse.com>
Date:	Tue, 21 Jun 2016 22:43:05 +0200
From:	Oliver Neukum <oneukum@...e.com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:	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

On Tue, 2016-06-21 at 16:58 +0300, Heikki Krogerus wrote:
> On Tue, Jun 21, 2016 at 03:08:52PM +0200, Oliver Neukum wrote:
>  
> > The firmware will surely want to display something. So it is possible
> > that we start the OS will a valid power contract. How do we deal
> > with that? Renegotiate?
> 
> Systems where the firmware has to negotiate PD will likely provide
> firmware interface like UCSI, and where the OS has no direct
> interaction with the USB PD transceiver. In these case there is no
> need to renegotiate as we are just reporting in OS the initial state
> after bootup.

How certain is that? I was under the impression that on many systems
the OS would speak to the TCPM directly.

> We do have a system where the typec port is used to power the board.
> On these systems the firmware does not communicate PD (so we will
> never have the firmware displaying anything over Type-C on those
> systems), but the USB PD chargers for example are detected as 3.0A
> Type-C power supplies before any USB PD negotiation takes place, just
> like the spec says, and that is more then enough to power these boards.

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.

	Regards
		Oliver