linux-kernel - Re: [char-misc-next 03/11] mei: bus: Initial implementation for I/O routines

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Message-Id: <201302111508.24317.arnd@arndb.de>
Date:	Mon, 11 Feb 2013 15:08:24 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Samuel Ortiz <sameo@...ux.intel.com>
Cc:	Tomas Winkler <tomas.winkler@...el.com>,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [char-misc-next 03/11] mei: bus: Initial implementation for I/O routines

On Monday 11 February 2013, Samuel Ortiz wrote:
> On Mon, Feb 11, 2013 at 11:52:42AM +0000, Arnd Bergmann wrote:
> > On Thursday 07 February 2013, Samuel Ortiz wrote:
> > > On Thu, Feb 07, 2013 at 10:34:44PM +0000, Arnd Bergmann wrote:
> > > > On Thursday 07 February 2013, Tomas Winkler wrote:
> > > > > +
> > > > > +struct mei_bus_ops {
> > > > > +       int (*send)(struct mei_bus_client *client, u8 *buf, size_t length);
> > > > > +       int (*recv)(struct mei_bus_client *client, u8 *buf, size_t length);
> > > > > +};
> > > > > +
> > > > 
> > > > Can you have more than one set of mei_bus_ops in a driver? 
> > > You can have at most one mei_bus_ops per mei_bus_client.
> > > 
> > > > If not, how about adding the callbacks to the mei_bus_driver structure
> > > > directly as a simplification? 
> > > I can add the ops directly to the mei_bus_client structure, yes.
> > 
> > I looked at the new version, and it's not what I assumed it would be.
> > I thought the operations were specific to a client driver and should
> > be part of the /mei_bus_driver/ structure, not the /mei_bus_client/.
> The ops should be part of mei_bus_client as they're specific to the MEI
> protocol for a given IP block on the ME. You need to have MEI and HECI
> knowledge to implement those ops and drivers (defining their mei_bus_driver
> structure) should not have that kind of knowledge but rather focus on the
> technology they're driving.
> If we take the NFC example again, the drivers/nfc/ code will send NFC payloads
> to the bus I/O routines and this is where the mei_bus_client ops will add the
> ME specific protocol (command and request id for the NFC block) on top of it.
> In practice, this is an additional header which handles a transport layer that's
> specific not only to the ME but to the NFC block of it. So each ME block can
> have its own protocol to send and receive technology specific payloads, that's
> what those ops implement.
> That's why I think that those ops should not be defined by the drivers/nfc/ code
> and in fact should be opaque to it.

I think I'm still confused. What I read in your description is that unlike
other subsystems that have a common bus implementation that is hooked into
by two kinds of drivers (bus drivers that provide devices like a USB host
controller, and device drivers that use those devices), you have three
components that can be mixed independently: the bus (based on which
PCI device you have), the transport and the endpoint device. Is that
correct?

If so, how do you know which transport to use?

	Arnd
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