diff mbox series

[1/2] kernel: usb: Autoprobe g_serial

Message ID 20231111-dns313-usb-serial-v1-1-6402033bcdfb@linaro.org
State Rejected, archived
Delegated to: Linus Walleij
Headers show
Series Enable USB serial console on the D-Link DNS-313 | expand

Commit Message

Linus Walleij Nov. 11, 2023, 10:02 p.m. UTC
For devices using USB gadget serial we need to probe the modules
usb_f_acm and g_serial in order, then the available UDC (USB device
controller) interface will be hooked up to a serial port as
/dev/ttyGS0. (On the host side this appears as /dev/ttyACM0
when plugging in the USB cable.)

I don't quite understand why this wasn't done before for the
module explicitly called kmod-usb-serial.

Before this patch we have to enter a console and type

  modprobe g_serial

To get a serial console on /dev/ttyGS0, after this it is
automatic.

Since you might only have the serial console, it is a bit
catch 22 to have to use a serial console to activate the
serial console.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 package/kernel/linux/modules/usb.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Chuanhong Guo Nov. 19, 2023, 1:26 p.m. UTC | #1
Hi!

On Sun, Nov 12, 2023 at 6:04 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> For devices using USB gadget serial we need to probe the modules
> usb_f_acm and g_serial in order, then the available UDC (USB device
> controller) interface will be hooked up to a serial port as
> /dev/ttyGS0. (On the host side this appears as /dev/ttyACM0
> when plugging in the USB cable.)
>
> I don't quite understand why this wasn't done before for the
> module explicitly called kmod-usb-serial.

The g_*.ko gadget modules conflict with each other. I think
it isn't loaded by default to prevent that when users decided
to install multiple of them.

I made an init script to setup USB gadget using the "modern"
configfs approach:
https://github.com/openwrt/openwrt/pull/14005
Maybe you can make use of this one instead? :)
Lech Perczak Nov. 19, 2023, 4:49 p.m. UTC | #2
Hi Linus,

W dniu 2023-11-11 o 23:02, Linus Walleij pisze:
> For devices using USB gadget serial we need to probe the modules
> usb_f_acm and g_serial in order, then the available UDC (USB device
> controller) interface will be hooked up to a serial port as
> /dev/ttyGS0. (On the host side this appears as /dev/ttyACM0
> when plugging in the USB cable.)
>
> I don't quite understand why this wasn't done before for the
> module explicitly called kmod-usb-serial.
>
> Before this patch we have to enter a console and type
>
>    modprobe g_serial
>
> To get a serial console on /dev/ttyGS0, after this it is
> automatic.
>
> Since you might only have the serial console, it is a bit
> catch 22 to have to use a serial console to activate the
> serial console.
>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
>   package/kernel/linux/modules/usb.mk | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/package/kernel/linux/modules/usb.mk b/package/kernel/linux/modules/usb.mk
> index 0a5f5a8993c9..f54dc4380737 100644
> --- a/package/kernel/linux/modules/usb.mk
> +++ b/package/kernel/linux/modules/usb.mk
> @@ -207,7 +207,7 @@ define KernelPackage/usb-gadget-serial
>   	$(LINUX_DIR)/drivers/usb/gadget/function/usb_f_obex.ko \
>   	$(LINUX_DIR)/drivers/usb/gadget/function/usb_f_serial.ko \
>   	$(LINUX_DIR)/drivers/usb/gadget/legacy/g_serial.ko
> -  AUTOLOAD:=$(call AutoLoad,52,usb_f_acm)
> +  AUTOLOAD:=$(call AutoLoad,52,usb_f_acm g_serial)
>     $(call AddDepends/usb)
>   endef
>   
>
I think I know the reason why it isn't the case. 
kmod-usb-gadget-cdc-composite which pulls both kmod-usb-gadget-serial 
and kmod-usb-gadget-eth packages, and including autoprobingf g_serial 
within this would clash with that. I think the gadget configuration 
itself (apart from implementation) could be packaged separately and 
included as device packages, pulling needed dependencies. And something 
like that just appeared on Github: 
https://github.com/openwrt/openwrt/pull/14005/
Linus Walleij Nov. 24, 2023, 9:56 a.m. UTC | #3
On Sun, Nov 19, 2023 at 2:27 PM Chuanhong Guo <gch981213@gmail.com> wrote:
> On Sun, Nov 12, 2023 at 6:04 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> >
> > For devices using USB gadget serial we need to probe the modules
> > usb_f_acm and g_serial in order, then the available UDC (USB device
> > controller) interface will be hooked up to a serial port as
> > /dev/ttyGS0. (On the host side this appears as /dev/ttyACM0
> > when plugging in the USB cable.)
> >
> > I don't quite understand why this wasn't done before for the
> > module explicitly called kmod-usb-serial.
>
> The g_*.ko gadget modules conflict with each other. I think
> it isn't loaded by default to prevent that when users decided
> to install multiple of them.
>
> I made an init script to setup USB gadget using the "modern"
> configfs approach:
> https://github.com/openwrt/openwrt/pull/14005
> Maybe you can make use of this one instead? :)

This is a step in the right direction as it moves toward using configfs
as is custom these days, approved.

I think I would need an example of how to utilize this for the serial
gadget though...

Yours,
Linus Walleij
diff mbox series

Patch

diff --git a/package/kernel/linux/modules/usb.mk b/package/kernel/linux/modules/usb.mk
index 0a5f5a8993c9..f54dc4380737 100644
--- a/package/kernel/linux/modules/usb.mk
+++ b/package/kernel/linux/modules/usb.mk
@@ -207,7 +207,7 @@  define KernelPackage/usb-gadget-serial
 	$(LINUX_DIR)/drivers/usb/gadget/function/usb_f_obex.ko \
 	$(LINUX_DIR)/drivers/usb/gadget/function/usb_f_serial.ko \
 	$(LINUX_DIR)/drivers/usb/gadget/legacy/g_serial.ko
-  AUTOLOAD:=$(call AutoLoad,52,usb_f_acm)
+  AUTOLOAD:=$(call AutoLoad,52,usb_f_acm g_serial)
   $(call AddDepends/usb)
 endef