linux-kernel - Re: [PATCH 1/3] tty/serial: Add RISC-V SBI earlycon support

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Date:   Fri, 07 Dec 2018 10:30:27 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     anup@...infault.org
CC:     Greg KH <gregkh@...uxfoundation.org>, jslaby@...e.com,
        aou@...s.berkeley.edu, atish.patra@....com,
        Christoph Hellwig <hch@...radead.org>, robh@...nel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org, anup@...infault.org
Subject:     Re: [PATCH 1/3] tty/serial: Add RISC-V SBI earlycon support

On Tue, 04 Dec 2018 05:55:05 PST (-0800), anup@...infault.org wrote:
> In RISC-V, the M-mode runtime firmware provide SBI calls for
> debug prints. This patch adds earlycon support using RISC-V
> SBI console calls. To enable it, just pass "earlycon=sbi" in
> kernel parameters.
>
> Signed-off-by: Anup Patel <anup@...infault.org>
> ---
>  drivers/tty/serial/Kconfig              | 12 +++++++++++
>  drivers/tty/serial/Makefile             |  1 +
>  drivers/tty/serial/earlycon-riscv-sbi.c | 28 +++++++++++++++++++++++++
>  3 files changed, 41 insertions(+)
>  create mode 100644 drivers/tty/serial/earlycon-riscv-sbi.c
>
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 32886c304641..287bb41ac814 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -85,6 +85,18 @@ config SERIAL_EARLYCON_ARM_SEMIHOST
>  	  with "earlycon=smh" 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
> +	select SERIAL_CORE
> +	select SERIAL_CORE_CONSOLE
> +	select SERIAL_EARLYCON
> +	help
> +	  Support for early debug console using RISC-V SBI. This enables
> +	  the console before standard serial driver is probed. This is enabled
> +	  with "earlycon=sbi" on the kernel command line. The console is
> +	  enabled when early_param is processed.
> +
>  config SERIAL_SB1250_DUART
>  	tristate "BCM1xxx on-chip DUART serial support"
>  	depends on SIBYTE_SB1xxx_SOC=y
> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> index daac675612df..3ce26ce08616 100644
> --- a/drivers/tty/serial/Makefile
> +++ b/drivers/tty/serial/Makefile
> @@ -7,6 +7,7 @@ obj-$(CONFIG_SERIAL_CORE) += serial_core.o
>
>  obj-$(CONFIG_SERIAL_EARLYCON) += earlycon.o
>  obj-$(CONFIG_SERIAL_EARLYCON_ARM_SEMIHOST) += earlycon-arm-semihost.o
> +obj-$(CONFIG_SERIAL_EARLYCON_RISCV_SBI) += earlycon-riscv-sbi.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-riscv-sbi.c b/drivers/tty/serial/earlycon-riscv-sbi.c
> new file mode 100644
> index 000000000000..e1a551aae336
> --- /dev/null
> +++ b/drivers/tty/serial/earlycon-riscv-sbi.c
> @@ -0,0 +1,28 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * RISC-V SBI based earlycon
> + *
> + * Copyright (C) 2018 Anup Patel <anup@...infault.org>
> + */
> +#include <linux/kernel.h>
> +#include <linux/console.h>
> +#include <linux/init.h>
> +#include <linux/serial_core.h>
> +#include <asm/sbi.h>
> +
> +static void sbi_console_write(struct console *con,
> +			      const char *s, unsigned int n)
> +{
> +	int i;
> +
> +	for (i = 0; i < n; ++i)
> +		sbi_console_putchar(s[i]);
> +}
> +
> +static int __init early_sbi_setup(struct earlycon_device *device,
> +				  const char *opt)
> +{
> +	device->con->write = sbi_console_write;
> +	return 0;
> +}
> +EARLYCON_DECLARE(sbi, early_sbi_setup);

Reviewed-by: Palmer Dabbelt <palmer@...ive.com>