Re: [PATCH v2 6/8] xen/riscv: introduce early_printk basic stuff

[Alistair Francis <alistair23@xxxxxxxxx>]

On Tue, Jan 10, 2023 at 1:47 AM Oleksii Kurochko
<oleksii.kurochko@xxxxxxxxx> wrote:
>
> The patch introduces a basic stuff of early_printk functionality
> which will be enough to print 'hello from C environment".
> early_printk() function was changed in comparison with original as
> common isn't being built now so there is no vscnprintf.
>
> Because printk() relies on a serial driver (like the ns16550 driver)
> and drivers require working virtual memory (ioremap()) there is not
> print functionality early in Xen boot.
>
> This commit adds early printk implementation built on the putc SBI call.
>
> As sbi_console_putchar() is being already planned for deprecation
> it is used temporary now and will be removed or reworked after
> real uart will be ready.

There was a discussion to add a new SBI putchar replacement. It
doesn't seem to be completed yet, but there might be an SBI
replacement for this in the future as well.

Alistair

>
> Signed-off-by: Bobby Eshleman <bobby.eshleman@xxxxxxxxx>
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> ---
> Changes in V2:
>     - add license to early_printk.c
>     - add signed-off-by Bobby
>     - add RISCV_32 to Kconfig.debug to EARLY_PRINTK config
>     - update commit message
>     - order the files alphabetically in Makefile
> ---
>  xen/arch/riscv/Kconfig.debug              |  7 +++++
>  xen/arch/riscv/Makefile                   |  1 +
>  xen/arch/riscv/early_printk.c             | 33 +++++++++++++++++++++++
>  xen/arch/riscv/include/asm/early_printk.h | 12 +++++++++
>  4 files changed, 53 insertions(+)
>  create mode 100644 xen/arch/riscv/early_printk.c
>  create mode 100644 xen/arch/riscv/include/asm/early_printk.h
>
> diff --git a/xen/arch/riscv/Kconfig.debug b/xen/arch/riscv/Kconfig.debug
> index e69de29bb2..6ba0bd1e5a 100644
> --- a/xen/arch/riscv/Kconfig.debug
> +++ b/xen/arch/riscv/Kconfig.debug
> @@ -0,0 +1,7 @@
> +config EARLY_PRINTK
> +    bool "Enable early printk config"
> +    default DEBUG
> +    depends on RISCV_64 || RISCV_32
> +    help
> +
> +      Enables early printk debug messages
> diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
> index fd916e1004..1a4f1a6015 100644
> --- a/xen/arch/riscv/Makefile
> +++ b/xen/arch/riscv/Makefile
> @@ -1,3 +1,4 @@
> +obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
>  obj-$(CONFIG_RISCV_64) += riscv64/
>  obj-y += sbi.o
>  obj-y += setup.o
> diff --git a/xen/arch/riscv/early_printk.c b/xen/arch/riscv/early_printk.c
> new file mode 100644
> index 0000000000..88da5169ed
> --- /dev/null
> +++ b/xen/arch/riscv/early_printk.c
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * RISC-V early printk using SBI
> + *
> + * Copyright (C) 2021 Bobby Eshleman <bobbyeshleman@xxxxxxxxx>
> + */
> +#include <asm/sbi.h>
> +#include <asm/early_printk.h>
> +
> +/*
> + * TODO:
> + *   sbi_console_putchar is already planned for deprication
> + *   so it should be reworked to use UART directly.
> +*/
> +void early_puts(const char *s, size_t nr)
> +{
> +    while ( nr-- > 0 )
> +    {
> +        if (*s == '\n')
> +            sbi_console_putchar('\r');
> +        sbi_console_putchar(*s);
> +        s++;
> +    }
> +}
> +
> +void early_printk(const char *str)
> +{
> +    while (*str)
> +    {
> +        early_puts(str, 1);
> +        str++;
> +    }
> +}
> diff --git a/xen/arch/riscv/include/asm/early_printk.h 
> b/xen/arch/riscv/include/asm/early_printk.h
> new file mode 100644
> index 0000000000..05106e160d
> --- /dev/null
> +++ b/xen/arch/riscv/include/asm/early_printk.h
> @@ -0,0 +1,12 @@
> +#ifndef __EARLY_PRINTK_H__
> +#define __EARLY_PRINTK_H__
> +
> +#include <xen/early_printk.h>
> +
> +#ifdef CONFIG_EARLY_PRINTK
> +void early_printk(const char *str);
> +#else
> +static inline void early_printk(const char *s) {};
> +#endif
> +
> +#endif /* __EARLY_PRINTK_H__ */
> --
> 2.38.1
>
>