linux-kernel - Re: [PATCH 2/3] usb: type-c: USB Type-C Connector System Software Interface

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Message-ID: <87twl6qpim.fsf@ti.com>
Date:	Thu, 18 Feb 2016 12:30:41 +0200
From:	Felipe Balbi <balbif@...il.com>
To:	Oliver Neukum <oneukum@...e.com>, Felipe Balbi <balbif@...il.com>
Cc:	Felipe Balbi <balbi@...nel.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 2/3] usb: type-c: USB Type-C Connector System Software Interface


Hi,

Oliver Neukum <oneukum@...e.com> writes:
>> > What exactly are you sure about about?
>> 
>> heh, missed a NOT there :-)
>
> I am still confused :-)
> Do you think a sysfs interface is good, bad or good
> but insufficient?

I'm not sure it's the best interface. My fear is that as new
requirements/features come along, the amount of files will continue to
grow.

>> I guess what I'm trying to say is that CC microcontroller might not be
>> the one controlling the multiplexer which switches USB pins to another
>> function. IOW:
>> 
>> Change to alternate mode X message
>>  CC microcontroller interrupts CPU
>>   read status to get X
>>    change multiplexer
>> 
>
> Yes. But it seems to me that in this case we need a kernel driver
> without an API to user space. There are necessarily internal users

that assumes kernel always knows all possible alternate modes. What do
we about bogus requests (request alternate mode X when X is not
supported) ?

> of the PD controller. There are also external users. So the CC pins
> should be seen as a bus, which in essence they are (it reminds me
> of ancient ethernet actually), and if you really want full user
> space access, you'd need the quivalent of an sg driver.
>
> The issue is orthogonal to the question how we support UCSI, except
> that UCSI is a user of the CC pins and PD and frankly I don't see the
> firmware and a driver access this sanely simultaneously.  Therefore
> I'd prefer we make an API here which does not depend on UCSI, but can,
> if necessary, work on top of a driver doing full hardware access.

fair enough.

-- 
balbi

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