Re: [RFC PATCH 5/6] xen/riscv: Add early_printk

[Alistair Francis <alistair23@xxxxxxxxx>]

On Tue, May 31, 2022 at 5:09 PM Xie Xun <xiexun162534@xxxxxxxxx> wrote:
>
> Signed-off-by: Xie Xun <xiexun162534@xxxxxxxxx>
> ---
>  xen/arch/riscv/Makefile                   |  1 +
>  xen/arch/riscv/early_printk.c             | 48 +++++++++++++++++++++++
>  xen/arch/riscv/include/asm/early_printk.h | 10 +++++
>  3 files changed, 59 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/Makefile b/xen/arch/riscv/Makefile
> index c61349818f..f9abc8401b 100644
> --- a/xen/arch/riscv/Makefile
> +++ b/xen/arch/riscv/Makefile
> @@ -3,6 +3,7 @@ obj-y += lib/
>  obj-y   += domctl.o
>  obj-y   += domain.o
>  obj-y   += delay.o
> +obj-y   += early_printk.o
>  obj-y   += guestcopy.o
>  obj-y   += irq.o
>  obj-y   += p2m.o
> diff --git a/xen/arch/riscv/early_printk.c b/xen/arch/riscv/early_printk.c
> new file mode 100644
> index 0000000000..81d69add01
> --- /dev/null
> +++ b/xen/arch/riscv/early_printk.c

This should be named differently. This file should be called
`sbi_console_early_printk.c` to better indicate that it's using the
sbi_console

The SBI print functions are useful, but they have been marked as
deprecated with no future replacement (see
https://github.com/riscv-non-isa/riscv-sbi-doc/blob/659950dc57f9840cf8242c1cff138c2ee67634bb/riscv-sbi.adoc#5-legacy-extensions-eids-0x00---0x0f)

For the initial port I think it's ok to use these, but this isn't a
long term solution, we should aim to migrate to using the standard
hardware UART.

I'm sure Xen already has a driver for the ns16550 UART so it might be
worth just using that directly and not worrying with the sbi_console.

Alistair

> @@ -0,0 +1,48 @@
> +/*
> + * RISC-V early printk using SBI
> + *
> + * Copyright (C) 2021 Bobby Eshleman <bobbyeshleman@xxxxxxxxx>
> + */
> +#include <asm/sbi.h>
> +#include <asm/early_printk.h>
> +#include <xen/stdarg.h>
> +#include <xen/lib.h>
> +
> +void _early_puts(const char *s, size_t nr)
> +{
> +    while ( nr-- > 0 )
> +    {
> +        if (*s == '\n')
> +            sbi_console_putchar('\r');
> +        sbi_console_putchar(*s);
> +        s++;
> +    }
> +}
> +
> +static void vprintk_early(const char *prefix, const char *fmt, va_list args)
> +{
> +    char buf[128];
> +    int sz;
> +
> +    early_puts(prefix);
> +
> +    sz = vscnprintf(buf, sizeof(buf), fmt, args);
> +
> +    if ( sz < 0 ) {
> +        early_puts("(XEN) vprintk_early error\n");
> +        return;
> +    }
> +
> +    if ( sz == 0 )
> +        return;
> +
> +    _early_puts(buf, sz);
> +}
> +
> +void early_printk(const char *fmt, ...)
> +{
> +    va_list args;
> +    va_start(args, fmt);
> +    vprintk_early("(XEN) ", fmt, args);
> +    va_end(args);
> +}
> 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..0d9928b333
> --- /dev/null
> +++ b/xen/arch/riscv/include/asm/early_printk.h
> @@ -0,0 +1,10 @@
> +#ifndef __EARLY_PRINTK_H__
> +#define __EARLY_PRINTK_H__
> +
> +#include <xen/string.h>
> +
> +#define early_puts(s) _early_puts((s), strlen((s)))
> +void _early_puts(const char *s, size_t nr);
> +void early_printk(const char *fmt, ...);
> +
> +#endif /* __EARLY_PRINTK_H__ */
> --
> 2.30.2
>
>