Devicetree binding for omap3-serial & bcm2048 combination

Nokia N900 contains bluetooth module connected on serial
port. Unfortunately, serial and bluetooth are rather closely coupled,
so standard serial driver can not be used, and we really don't want
/dev/ttyS1 to be published for internal port of bluetooth
stack... Hence solution below.

Signed-off-by: Pavel Machek <pavel@ucw.cz>

Hi,

On Wed, Jan 28, 2015 at 10:35:01AM +0100, Pavel Machek wrote:
> Nokia N900 contains bluetooth module connected on serial
> port. Unfortunately, serial and bluetooth are rather closely coupled,
> so standard serial driver can not be used, and we really don't want
> /dev/ttyS1 to be published for internal port of bluetooth
> stack... Hence solution below.

Actually that's not true. If one takes a deeper look into Nokia's
bcm2048 driver one can see, that it's using more or less the same
protocol as other bluetooth modules (H4) with some custom
extensions. The only special thing are two additional GPIOs, which
are enabled before sending data, so that the bluetooth chip and the
omap can wakeup each other. I don't think one can speak of "closely
coupled" for this.

The only reason you needed this hacked DT binding is, that you do
not want to properly fix the bcm2048 driver, so that it can use the
omap-serial driver.

-- Sebastian

On Wed, Jan 28, 2015 at 09:35:01AM +0000, Pavel Machek wrote:
> Nokia N900 contains bluetooth module connected on serial
> port. Unfortunately, serial and bluetooth are rather closely coupled,
> so standard serial driver can not be used, and we really don't want
> /dev/ttyS1 to be published for internal port of bluetooth
> stack... Hence solution below.

How are they closely coupled?

> Signed-off-by: Pavel Machek <pavel@ucw.cz>
> 
> diff --git a/Documentation/devicetree/bindings/serial/omap_serial.txt b/Documentation/devicetree/bindings/serial/omap_serial.txt
> index 342eedd..e9fde42 100644
> --- a/Documentation/devicetree/bindings/serial/omap_serial.txt
> +++ b/Documentation/devicetree/bindings/serial/omap_serial.txt
> @@ -4,7 +4,14 @@ Required properties:
>  - compatible : should be "ti,omap2-uart" for OMAP2 controllers
>  - compatible : should be "ti,omap3-uart" for OMAP3 controllers
>  - compatible : should be "ti,omap4-uart" for OMAP4 controllers
> +- compatible : should be "ti+brcm,omap3-uart,bcm2048" for bcm2048
> +	       bluetooth connected to OMAP3 serial

I'm very much not keen on munging the two devices into one.

Elsewhere Neil Brown and others having been looking into allowing UARTs
to function as busses for single devices, which to me seems to cover
this case.

Mark.

>  - ti,hwmods : Must be "uart<n>", n being the instance number (1-based)
>  
>  Optional properties:
>  - clock-frequency : frequency of the clock input to the UART
> +
> +Required properties for ti+brcm,omap3-uart,bcm2048:
> +- reset-gpios : gpio for reset pin
> +- host-wakeup-gpios : gpio for host wakeup
> +- bluetooth-wakeup-gpios : gpio for bluetooth wakeup
> 
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
> 
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