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 <20231027182650.281405-8-jiaxun.yang@flygoat.com>
Date:   Fri, 27 Oct 2023 21:48:44 +0100
From:   "Jiaxun Yang" <jiaxun.yang@flygoat.com>
To:     "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>
Cc:     linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Thomas Bogendoerfer" <tsbogend@alpha.franken.de>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        jirislaby@kernel.org
Subject: Re: [PATCH 3/3] serial: Add an earlycon driver for MIPS UHI semihosting
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=E5=9C=A82023=E5=B9=B410=E6=9C=8827=E6=97=A5=E5=8D=81=E6=9C=88 =E4=B8=8B=
=E5=8D=887:26=EF=BC=8CJiaxun Yang=E5=86=99=E9=81=93=EF=BC=9A
> UHI is MIPS's implementation of semihosting.
> Add an earlycon driver to help with debugging on boot.
>
> This driver is capable for print log using UHI's "Plog" or interact
> with KGDB using UHI's stdio function.
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> ---
>  drivers/tty/serial/Kconfig             | 13 ++++
>  drivers/tty/serial/Makefile            |  1 +
>  drivers/tty/serial/earlycon-mips-uhi.c | 85 ++++++++++++++++++++++++++
>  3 files changed, 99 insertions(+)
>  create mode 100644 drivers/tty/serial/earlycon-mips-uhi.c
>
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index bdc568a4ab66..04c62c6b45cd 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -85,6 +85,19 @@ config SERIAL_EARLYCON_SEMIHOST
>  	  This is enabled with "earlycon=3Dsmh" on the kernel command line.
>  	  The console is enabled when early_param is processed.
>=20
> +config SERIAL_EARLYCON_UHI

^ Oops there is a symbol name mismatch, will fix in v2.

Sorry for the noise.

Thanks
- Jiaxun

> +	bool "Early console using MIPS UHI semihosting"
> +	depends on MIPS
> +	select SERIAL_CORE
> +	select SERIAL_CORE_CONSOLE
> +	select SERIAL_EARLYCON
> +	help
> +	  Support for early debug console using UHI semihosting.
> +	  This enables the console before standard serial driver is probed.
> +	  This is enabled with "earlycon=3Duhi" or "earlycon=3Duhi_stdio" on=
 the
> +	  kernel command line.
> +	  The console is enabled when early_param is processed.
> +
>  config SERIAL_EARLYCON_RISCV_SBI
>  	bool "Early console using RISC-V SBI"
>  	depends on RISCV_SBI_V01
> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> index f6b8c220dcfb..ef5e9c87aea1 100644
> --- a/drivers/tty/serial/Makefile
> +++ b/drivers/tty/serial/Makefile
> @@ -9,6 +9,7 @@ serial_base-y :=3D serial_core.o serial_base_bus.o=20
> serial_ctrl.o serial_port.o
>  obj-$(CONFIG_SERIAL_EARLYCON) +=3D earlycon.o
>  obj-$(CONFIG_SERIAL_EARLYCON_SEMIHOST) +=3D earlycon-semihost.o
>  obj-$(CONFIG_SERIAL_EARLYCON_RISCV_SBI) +=3D earlycon-riscv-sbi.o
> +obj-$(CONFIG_SERIAL_EARLYCON_MIPS_UHI) +=3D earlycon-mips-uhi.o
>=20
>  # 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-mips-uhi.c=20
> b/drivers/tty/serial/earlycon-mips-uhi.c
> new file mode 100644
> index 000000000000..002bb2c37064
> --- /dev/null
> +++ b/drivers/tty/serial/earlycon-mips-uhi.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * MIPS UHI semihosting based earlycon
> + *
> + * Copyright (C) 2023 Jiaxun Yang <jiaxun.yang@flygoat.com>
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/console.h>
> +#include <linux/init.h>
> +#include <linux/serial_core.h>
> +#include <asm/uhi.h>
> +
> +static int stdin_fd =3D -1;
> +static int stdout_fd =3D -1;
> +
> +static void uhi_plog_write(struct console *con, const char *s,=20
> unsigned int n)
> +{
> +	uhi_plog(s, 0);
> +}
> +
> +static void uhi_stdout_write(struct console *con, const char *s,=20
> unsigned int n)
> +{
> +	if (stdout_fd < 0)
> +		return;
> +
> +	uhi_write(stdout_fd, s, n);
> +}
> +
> +#ifdef CONFIG_CONSOLE_POLL
> +static int uhi_stdin_read(struct console *con, char *s, unsigned int =
n)
> +{
> +	if (stdin_fd < 0)
> +		return 0;
> +
> +	return uhi_read(stdin_fd, s, n);
> +}
> +#endif
> +
> +static int uhi_stdio_fd_open(struct console *co, char *options)
> +{
> +	/*
> +	 * You have to open both stdin and stdout to get console work
> +	 * properly on some old CodeScape debugger.
> +	 */
> +	stdin_fd =3D uhi_open("/dev/stdin", UHI_O_RDONLY, 0);
> +	stdout_fd =3D uhi_open("/dev/stdout", UHI_O_WRONLY, 0);
> +
> +	return (stdin_fd < 0 || stdout_fd < 0) ? -ENODEV : 0;
> +}
> +
> +static int uhi_stdio_fd_close(struct console *co)
> +{
> +	int ret1 =3D 0, ret2 =3D 0;
> +
> +	if (stdin_fd >=3D 0)
> +		ret1 =3D uhi_close(stdin_fd);
> +	if (stdout_fd >=3D 0)
> +		ret2 =3D uhi_close(stdout_fd);
> +
> +	return (ret1 < 0 || ret2 < 0) ? -ENODEV : 0;
> +}
> +
> +static int
> +__init early_uhi_setup(struct earlycon_device *device, const char *op=
t)
> +{
> +	device->con->write =3D uhi_plog_write;
> +	return 0;
> +}
> +
> +static int
> +__init early_uhi_stdio_setup(struct earlycon_device *device, const=20
> char *opt)
> +{
> +
> +	device->con->setup =3D uhi_stdio_fd_open;
> +	device->con->exit =3D uhi_stdio_fd_close;
> +	device->con->write =3D uhi_stdout_write;
> +#ifdef CONFIG_CONSOLE_POLL
> +	device->con->read =3D uhi_stdin_read;
> +#endif
> +	return 0;
> +}
> +
> +EARLYCON_DECLARE(uhi, early_uhi_setup);
> +EARLYCON_DECLARE(uhi_stdio, early_uhi_stdio_setup);
> --=20
> 2.34.1

--=20
- Jiaxun