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

[Bobby Eshleman <bobby.eshleman@gmail.com>]

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On Mon, Jan 9, 2023 at 4:28 PM Alistair Francis <alistair23@gmail.com>
wrote:

> On Tue, Jan 10, 2023 at 1:47 AM Oleksii Kurochko
> <oleksii.kurochko@gmail.com> 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
>

Are you referring to the Debug Console Extension (EID #0x4442434E "DBCN")”?

https://lists.riscv.org/g/tech-prs/topic/96051183#84

Best,
Bobby


> >
> > Signed-off-by: Bobby Eshleman <bobby.eshleman@gmail.com>
> > Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> > ---
> > 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@gmail.com>
> > + */
> > +#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
> >
> >
>

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