Re: [PATCH v8 1/2] Serial: silabs si4455 serial driver

On Tue, Jan 12, 2021 at 05:13:16PM +0100, 'Greg Kroah-Hartman' wrote:

On Tue, Jan 12, 2021 at 03:43:22PM +0000, József Horváth wrote:

quoted

On Tue, Jan 12, 2021 at 11:28:08AM +0100, 'Greg Kroah-Hartman' wrote:

quoted

On Tue, Jan 12, 2021 at 10:18:33AM +0000, Jozsef Horvath wrote:

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--- a/include/uapi/linux/serial_core.h
+++ b/include/uapi/linux/serial_core.h

@@ -279,4 +279,7 @@
 /* Freescale LINFlexD UART */
 #define PORT_LINFLEXUART	122
 
+/* Silicon Labs SI4455 */
+#define PORT_SI4455     123

What userspace tool is going to need this value?

The PORT_SI4455 is defined for using as port type value in struct uart_port.
I checked other serial drivers under drivers/tty/serial and the port types
used by serial drivers are defined in two places:

include/uapi/linux/serial_core.h
include/uapi/linux/serial.h

The port type is required by serial_core, and its value goes back to
user space with TIOCGSERIAL ioctl call.

What is it required for?  Who uses this?

quoted

I can't set port type value to 0(PORT_UNKNOWN).

Why not?

In drivers/tty/serial/serial_core.c
1784:	uart_port_activate(...)
1799:		->	uart_startup(...)
260:			->	uart_port_startup(...)

183:	static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
184:			int init_hw)
...
191:		if (uport->type == PORT_UNKNOWN)
192:			return 1;
...
221:		retval = uport->ops->startup(uport);	<--This is the reason. The drivers
 startup function is not get called if type==PORT_UNKNOWN
...

quoted

I think my drivers source is not the best place to defining PORT_SI4455,
 but I can't find better place then include/uapi/linux/serial_core.h

Could you please help me where is the correct location for this definition?

I ask as I am trying to figure out why we keep adding these ids, yet no
tool that i know of seems to actually use them.

If you don't have a tool that needs to use a new id, then I would
recommend not adding it, right?

This definition is not my requirement, but I would avoid collision with other
 drivers port type value.
At this point as I understand your words, these definitions will be obsolete
 or optional soon and I can choose any value for drivers port type.

Right?

I would ask you about dev name (ttySSi).
Is it okay?

I didnt find any similar.

thanks,

greg k-h

Üdvözlettel / Best regards:
József Horváth