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

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Message-Id: <201012061615.28093.arnd@arndb.de>
Date:	Mon, 6 Dec 2010 16:15:27 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Vitaly Wool <vitalywool@...il.com>
Cc:	"Par-Gunnar Hjalmdahl" <pghatwork@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linus.walleij@...ricsson.com, linux-bluetooth@...r.kernel.org,
	linux-kernel@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [PATCH 5/9] mfd: Add UART support for the ST-Ericsson CG2900.

On Monday 06 December 2010, Vitaly Wool wrote:
> On Mon, Dec 6, 2010 at 3:06 PM, Arnd Bergmann <arnd@...db.de> wrote:
> 
> > hci_ll is not the line discipline but the a TI specific uart protocol.
> > The line discipline driver (hci_ldisc.c) is shared across all protocols
> > (h4, ll, ...) and gets extended slightly so it can deal with cg2900
> > in addition to the existing HCIs. The rest of the cg2900 support is
> > about adding more hci_uart_protos.
> 
> I was referring to hci_ll as to the line discipline driver, not the
> line discipline itself.
> 
> The thing is, there are different Bluetooth combo chips which use HCI
> to encapsulate commands to the sub-chips behind, and there's also the
> implementation for TI chip doing that which is in the mainline. So
> instead of keeping reinventing the wheel, I think it's fairly
> beneficial for everything if we finally agree on something that works
> for all the combo chips of the type.

Yes, that makes sense. I'm probably missing something here, but
it seems to me that hci_ll is only about the power management stuff
on TI (and broadcom, as you say) chips, and the multi-protocol
support is currently handled in hci_ldisc by allowing multiple
protocols like h4 and ll to be registered. It that correct?

One aspect that Par-Gunnar mentioned was that the multi-protocol
stuff for cg2900 and I suspect other similar devices would also
need to work with non-UART-based HCIs, which don't use hci_uart_proto
but would need something similar. Also, hci_uart is currently not
modular, e.g. you cannot build hci_ll as a loadable module
as you'd need for dynamic registration.

	Arnd
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