Re: [PATCH v2 2/3] serial: core: Add support for DEVNAME:0.0 style naming for kernel console

[Ilpo Järvinen]

On Tue, 12 Sep 2023, Tony Lindgren wrote:

> We can now add hardware based addressing to serial ports. Starting with
> commit 84a9582fd203 ("serial: core: Start managing serial controllers to
> enable runtime PM"), and all the related fixes to this commit, the serial
> core now knows to which serial port controller the ports are connected.
> 
> The serial ports can be addressed with DEVNAME:0.0 style naming. The names
> are something like 00:04:0.0 for a serial port on qemu, and something like
> 2800000.serial:0.0 on platform device using systems like ARM64 for example.
> 
> The DEVNAME is the unique serial port hardware controller device name, AKA
> the name for port->dev. The 0.0 are the serial core controller id and port
> id.
> 
> Typically 0.0 are used for each controller and port instance unless the
> serial port hardware controller has multiple controllers or ports.
> 
> Using DEVNAME:0.0 style naming actually solves two long term issues for
> addressing the serial ports:
> 
> 1. According to Andy Shevchenko, using DEVNAME:0.0 style naming fixes an
>    issue where depending on the BIOS settings, the kernel serial port ttyS
>    instance number may change if HSUART is enabled
> 
> 2. Device tree using architectures no longer necessarily need to specify
>    aliases to find a specific serial port, and we can just allocate the
>    ttyS instance numbers dynamically in whatever probe order
> 
> To do this, we need a custom init time parser for the console= command
> line option as printk already handles parsing it with console_setup().
> Also early_param() gets handled by console_setup() if "console" and
> "earlycon" are used.
> 
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
> ---
>  drivers/tty/serial/Makefile          |   3 +
>  drivers/tty/serial/serial_base.h     |  11 +++
>  drivers/tty/serial/serial_base_con.c | 133 +++++++++++++++++++++++++++
>  drivers/tty/serial/serial_core.c     |   4 +
>  4 files changed, 151 insertions(+)
>  create mode 100644 drivers/tty/serial/serial_base_con.c
> 
> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> --- a/drivers/tty/serial/Makefile
> +++ b/drivers/tty/serial/Makefile
> @@ -3,6 +3,9 @@
>  # Makefile for the kernel serial device drivers.
>  #
>  
> +# Parse kernel command line consoles before the serial drivers probe
> +obj-$(CONFIG_SERIAL_CORE_CONSOLE) += serial_base_con.o
> +
>  obj-$(CONFIG_SERIAL_CORE) += serial_base.o
>  serial_base-y := serial_core.o serial_base_bus.o serial_ctrl.o serial_port.o
>  
> diff --git a/drivers/tty/serial/serial_base.h b/drivers/tty/serial/serial_base.h
> --- a/drivers/tty/serial/serial_base.h
> +++ b/drivers/tty/serial/serial_base.h
> @@ -45,3 +45,14 @@ void serial_ctrl_unregister_port(struct uart_driver *drv, struct uart_port *port
>  
>  int serial_core_register_port(struct uart_driver *drv, struct uart_port *port);
>  void serial_core_unregister_port(struct uart_driver *drv, struct uart_port *port);
> +
> +#ifdef CONFIG_SERIAL_CORE_CONSOLE
> +int serial_base_add_preferred_console(struct uart_driver *drv,
> +				      struct uart_port *port);
> +#else
> +static inline int serial_base_add_preferred_console(struct uart_driver *drv,
> +						    struct uart_port *port)
> +{
> +	return 0;
> +}
> +#endif
> diff --git a/drivers/tty/serial/serial_base_con.c b/drivers/tty/serial/serial_base_con.c
> new file mode 100644
> --- /dev/null
> +++ b/drivers/tty/serial/serial_base_con.c
> @@ -0,0 +1,133 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Serial base console options handling
> + *
> + * Copyright (C) 2023 Texas Instruments Incorporated - https://www.ti.com/
> + * Author: Tony Lindgren <tony@xxxxxxxxxxx>
> + */
> +
> +#include <linux/init.h>
> +#include <linux/list.h>
> +#include <linux/kernel.h>
> +#include <linux/serial_core.h>
> +#include <linux/slab.h>
> +
> +#include "serial_base.h"
> +
> +static LIST_HEAD(serial_base_consoles);
> +
> +struct serial_base_console {
> +	struct list_head node;
> +	char *name;

Can't this be const char as too?

-- 
 i.


> +	char *opt;
> +};
> +
> +/*
> + * Adds a preferred console for a serial port if console=DEVNAME:0.0
> + * style addressing is used for the kernel command line. Translates
> + * from DEVNAME:0.0 to port->dev_name such as ttyS. Duplicates are
> + * ignored by add_preferred_console().
> + */
> +int serial_base_add_preferred_console(struct uart_driver *drv,
> +				      struct uart_port *port)
> +{
> +	struct serial_base_console *entry;
> +	char *port_match;
> +
> +	port_match = kasprintf(GFP_KERNEL, "%s:%i.%i", dev_name(port->dev),
> +			       port->ctrl_id, port->port_id);
> +	if (!port_match)
> +		return -ENOMEM;
> +
> +	list_for_each_entry(entry, &serial_base_consoles, node) {
> +		if (!strcmp(port_match, entry->name)) {
> +			add_preferred_console(drv->dev_name, port->line,
> +					      entry->opt);
> +			break;
> +		}
> +	}
> +
> +	kfree(port_match);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(serial_base_add_preferred_console);
> +
> +/* Adds a command line console to the list of consoles for driver probe time */
> +static int __init serial_base_add_con(char *name, char *opt)
> +{
> +	struct serial_base_console *con;
> +
> +	con = kzalloc(sizeof(*con), GFP_KERNEL);
> +	if (!con)
> +		return -ENOMEM;
> +
> +	con->name = kstrdup(name, GFP_KERNEL);
> +	if (!con->name)
> +		goto free_con;
> +
> +	if (opt) {
> +		con->opt = kstrdup(opt, GFP_KERNEL);
> +		if (!con->name)
> +			goto free_name;
> +	}
> +
> +	list_add_tail(&con->node, &serial_base_consoles);
> +
> +	return 0;
> +
> +free_name:
> +	kfree(con->name);
> +
> +free_con:
> +	kfree(con);
> +
> +	return -ENOMEM;
> +}
> +
> +/* Parse console name and options */
> +static int __init serial_base_parse_one(char *param, char *val,
> +					const char *unused, void *arg)
> +{
> +	char *opt;
> +
> +	if (strcmp(param, "console"))
> +		return 0;
> +
> +	if (!val)
> +		return 0;
> +
> +	opt = strchr(val, ',');
> +	if (opt) {
> +		opt[0] = '\0';
> +		opt++;
> +	}
> +
> +	if (!strlen(val))
> +		return 0;
> +
> +	return serial_base_add_con(val, opt);
> +}
> +
> +/*
> + * The "console=" option is handled by console_setup() in printk. We can't use
> + * early_param() as do_early_param() checks for "console" and "earlycon" options
> + * so console_setup() potentially handles console also early. Use parse_args().
> + */
> +static int __init serial_base_opts_init(void)
> +{
> +	char *command_line;
> +
> +	command_line = kstrdup(boot_command_line, GFP_KERNEL);
> +	if (!command_line)
> +		return -ENOMEM;
> +
> +	parse_args("Setting serial core console", command_line,
> +		   NULL, 0, -1, -1, NULL, serial_base_parse_one);
> +
> +	kfree(command_line);
> +
> +	return 0;
> +}
> +
> +arch_initcall(serial_base_opts_init);
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -3358,6 +3358,10 @@ int serial_core_register_port(struct uart_driver *drv, struct uart_port *port)
>  	if (ret)
>  		goto err_unregister_ctrl_dev;
>  
> +	ret = serial_base_add_preferred_console(drv, port);
> +	if (ret)
> +		goto err_unregister_port_dev;
> +
>  	ret = serial_core_add_one_port(drv, port);
>  	if (ret)
>  		goto err_unregister_port_dev;
>