Re: [PATCH 7/8] tty/serial: add arm64 semihosting earlycon

[Nicolas Pitre]

On Fri, 21 Mar 2014, Rob Herring wrote:

> From: Rob Herring <robh@xxxxxxxxxx>
> 
> Add earlycon support for the arm64 semihosting debug serial interface.
> This allows enabling a debug console when early_params are processed.
> This is based on the arm64 earlyprintk smh support and is intended to
> replace it.
> 
> This is named arm rather than arm64 in hopes it will be used for both,
> but only arm64 is supported ATM.

It can't be used for both as the semihosting calls themselves need 
assembly code and this is not compatible with the equivalent ARM32 
calls.  So I'd suggest naming this "arm64" to avoid potential confusion.

> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Jiri Slaby <jslaby@xxxxxxx>
> ---
>  Documentation/kernel-parameters.txt        |  1 +
>  drivers/tty/serial/Kconfig                 | 17 +++++++++---
>  drivers/tty/serial/Makefile                |  1 +
>  drivers/tty/serial/earlycon-arm-semihost.c | 44 ++++++++++++++++++++++++++++++
>  4 files changed, 59 insertions(+), 4 deletions(-)
>  create mode 100644 drivers/tty/serial/earlycon-arm-semihost.c
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 81bdd52..e96e2ba 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -888,6 +888,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  		uart[8250],mmio,<addr>[,options]
>  		uart[8250],mmio32,<addr>[,options]
>  		pl011,<addr>
> +		smh
>  			Start an early, polled-mode console on a serial port
>  			at the specified I/O port or MMIO address. 8250
>  			MMIO inter-register address stride is either 8-bit
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 1685189..8b8f40e 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -14,6 +14,15 @@ config SERIAL_EARLYCON
>  	  the console before standard serial driver is probed. The console is
>  	  enabled when early_param is processed.
>  
> +config SERIAL_EARLYCON_ARM_SEMIHOST
> +	bool "Early console using ARM64 semihosting"
> +	depends on ARM64
> +	help
> +	  Support for early debug console using ARM64 semihosting. This enables
> +	  the console before standard serial driver is probed. This is enabled
> +	  with "earlycon=smh" on the kernel command line. The console is
> +	  enabled when early_param is processed.
> +
>  source "drivers/tty/serial/8250/Kconfig"
>  
>  comment "Non-8250 serial port support"
> @@ -230,7 +239,7 @@ config SERIAL_SAMSUNG_UARTS
>  	help
>  	  Select the number of available UART ports for the Samsung S3C
>  	  serial driver
> -	
> +
>  config SERIAL_SAMSUNG_DEBUG
>  	bool "Samsung SoC serial debug"
>  	depends on SERIAL_SAMSUNG && DEBUG_LL
> @@ -666,8 +675,8 @@ config PDC_CONSOLE
>  	depends on PARISC && !SERIAL_MUX && VT
>  	default n
>  	help
> -	  Saying Y here will enable the software based PDC console to be 
> -	  used as the system console.  This is useful for machines in 
> +	  Saying Y here will enable the software based PDC console to be
> +	  used as the system console.  This is useful for machines in
>  	  which the hardware based console has not been written yet.  The
>  	  following steps must be competed to use the PDC console:
>  
> @@ -858,7 +867,7 @@ config SERIAL_CPM
>  	depends on CPM2 || 8xx
>  	select SERIAL_CORE
>  	help
> -	  This driver supports the SCC and SMC serial ports on Motorola 
> +	  This driver supports the SCC and SMC serial ports on Motorola
>  	  embedded PowerPC that contain a CPM1 (8xx) or CPM2 (8xxx)
>  
>  config SERIAL_CPM_CONSOLE
> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> index 8af1415..9965b65 100644
> --- a/drivers/tty/serial/Makefile
> +++ b/drivers/tty/serial/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_SERIAL_CORE) += serial_core.o
>  obj-$(CONFIG_SERIAL_21285) += 21285.o
>  
>  obj-$(CONFIG_SERIAL_EARLYCON) += earlycon.o
> +obj-$(CONFIG_SERIAL_EARLYCON_ARM_SEMIHOST) += earlycon-arm-semihost.o
>  
>  # These Sparc drivers have to appear before others such as 8250
>  # which share ttySx minor node space.  Otherwise console device
> diff --git a/drivers/tty/serial/earlycon-arm-semihost.c b/drivers/tty/serial/earlycon-arm-semihost.c
> new file mode 100644
> index 0000000..fecec9a
> --- /dev/null
> +++ b/drivers/tty/serial/earlycon-arm-semihost.c
> @@ -0,0 +1,44 @@
> +/*
> + * Copyright (C) 2012 ARM Ltd.
> + * Author: Catalin Marinas <catalin.marinas@xxxxxxx>
> + *
> + * This program is free software: you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +#include <linux/kernel.h>
> +#include <linux/console.h>
> +#include <linux/init.h>
> +#include <linux/serial_core.h>
> +
> +/*
> + * Semihosting-based debug console
> + */
> +static void smh_putc(struct uart_port *port, int c)
> +{
> +	asm volatile("mov  x1, %0\n"
> +		     "mov  x0, #3\n"
> +		     "hlt  0xf000\n"
> +		     : : "r" (&c) : "x0", "x1", "memory");
> +}
> +
> +static void smh_write(struct console *con, const char *s, unsigned n)
> +{
> +	struct earlycon_device *dev = con->data;
> +	uart_console_write(&dev->port, s, n, smh_putc);
> +}
> +
> +int __init early_smh_setup(struct earlycon_device *device, const char *opt)
> +{
> +	device->con->write = smh_write;
> +	return 0;
> +}
> +EARLYCON_DECLARE(smh, early_smh_setup);
> -- 
> 1.8.3.2
> 
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