linux-kernel - Re: [PATCH 5/9] mfd: Add UART support for the ST-Ericsson CG2900.

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Date:	Mon, 6 Dec 2010 13:25:42 +0100
From:	Vitaly Wool <vitalywool@...il.com>
To:	Par-Gunnar Hjalmdahl <pghatwork@...il.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linus.walleij@...ricsson.com,
	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [PATCH 5/9] mfd: Add UART support for the ST-Ericsson CG2900.

Par,

> Well, from what I can see LL is an extension of the H4, basically it
> adds sleep mode handling in a vendor specific way to the normal H4
> protocol. So it is also based on the hci_h4 just as our file is. But
> our file has basically nothing in common with what has been for the LL
> file. We don't support any of the LL sleep commands for example.
> So if I would make a driver for a combo chip supporting LL, I would
> either modify the existing hci_ll.c or I would make a new file based
> on hci_ll.c. There is not much you could really reuse from our new
> file. Basically it would be the handling of any common channels, so if
> you would for example have the same specification of FM and GPS you
> could maybe save around 20 lines of common code, but you would
> probably have to add a lot of more code just to keep the solution
> generic.

Right, but this gives me the hard time seeing how your implementation
is applicable to other multi-functional chips with similar
functionality.

> One major difference is also that hci_ll never changes baud rate or
> other settings. I assume that is done from hciattach during startup
> instead. But we cannot run with that since we have to shut down the
> chip when no user is connected in order to save power. This means that
> we have to add vendor specific commands in order to for example set
> baud rate. And then you run into these vendor specific problems. If
> there would be a standardized specification on how to set baud rate
> and how to put chip in sleep I assume things could be solved
> differently, but that is not the case.

Again, there are at least TI and Broadcom chips that support HCI_LL
and if they were to use your implementation of the core, they would
have had to add 2 more implementations of the corresponding line
discipline driver.

> As a quick answer to your question: that would depend on the
> difference between the different controllers, I guess. But CG2900
> doesn't support the LL protocol so it is not an issue for that.

Right, but if you are only aiming cg2000, why would you create a
framework for that?  I initially thought your solution was generic
enough to handle other "many-in-one" Bluetooth chips but I'm
completely unsure about that now.

Thanks,
   Vitaly
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