Hi,

On Wed, Apr 19, 2017 at 07:50:18PM +0200, Arnd Bergmann wrote:
> With CONFIG_SERIAL_DEV_BUS=m, the hci_serdev.o file does not actually
> get built into hci_uart.o as the Makefile doesn't pick it up, leading
> to a link error with anything referring to it:
> 
> ERROR: "hci_uart_register_device" [drivers/bluetooth/hci_nokia.ko] undefined!
> scripts/Makefile.modpost:91: recipe for target '__modpost' failed
> 
> Changing this in the Makefile would cause another problem when
> hci_uart itself is built-in and cannot reference symbols from the
> serdev module.
> 
> This tries to address both problems by introducing a new hidden
> Kconfig symbol that controls both the compilation of hci_serdev.o
> and whether the Nokia driver can be selected. This seems to address
> the problem for me, though there might be a better way to do it.
> 
> Fixes: 7bb318680e86 ("Bluetooth: add nokia driver")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/bluetooth/Kconfig  | 8 +++++++-
>  drivers/bluetooth/Makefile | 2 +-
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bluetooth/Kconfig b/drivers/bluetooth/Kconfig
> index 8aafbed9e160..737d93ef27c5 100644
> --- a/drivers/bluetooth/Kconfig
> +++ b/drivers/bluetooth/Kconfig
> @@ -76,6 +76,12 @@ config BT_HCIUART
>  	  Say Y here to compile support for Bluetooth UART devices into the
>  	  kernel or say M to compile it as module (hci_uart).
>  
> +config BT_HCIUART_SERDEV
> +	bool
> +	depends on SERIAL_DEV_BUS && BT_HCIUART
> +	depends on SERIAL_DEV_BUS=y || SERIAL_DEV_BUS=BT_HCIUART
> +	default y
> +
>  config BT_HCIUART_H4
>  	bool "UART (H4) protocol support"
>  	depends on BT_HCIUART
> @@ -89,7 +95,7 @@ config BT_HCIUART_H4
>  config BT_HCIUART_NOKIA
>  	tristate "UART Nokia H4+ protocol support"
>  	depends on BT_HCIUART

I guess BT_HCIUART dependency is no longer needed
when we have BT_HCIUART_SERDEV dependency?

Otherwise:

Reviewed-by: Sebastian Reichel <sre@kernel.org>

> -	depends on SERIAL_DEV_BUS
> +	depends on BT_HCIUART_SERDEV
>  	depends on PM
>  	help
>  	  Nokia H4+ is serial protocol for communication between Bluetooth
> diff --git a/drivers/bluetooth/Makefile b/drivers/bluetooth/Makefile
> index a7f237320f4b..e693ca6eeed9 100644
> --- a/drivers/bluetooth/Makefile
> +++ b/drivers/bluetooth/Makefile
> @@ -31,7 +31,7 @@ btmrvl-y			:= btmrvl_main.o
>  btmrvl-$(CONFIG_DEBUG_FS)	+= btmrvl_debugfs.o
>  
>  hci_uart-y				:= hci_ldisc.o
> -hci_uart-$(CONFIG_SERIAL_DEV_BUS)	+= hci_serdev.o
> +hci_uart-$(CONFIG_BT_HCIUART_SERDEV)	+= hci_serdev.o
>  hci_uart-$(CONFIG_BT_HCIUART_H4)	+= hci_h4.o
>  hci_uart-$(CONFIG_BT_HCIUART_BCSP)	+= hci_bcsp.o
>  hci_uart-$(CONFIG_BT_HCIUART_LL)	+= hci_ll.o
> -- 
> 2.9.0
>