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

[Alistair Francis <alistair23@xxxxxxxxx>]

On Tue, Jan 10, 2023 at 5:29 PM Bobby Eshleman <bobby.eshleman@xxxxxxxxx> wrote:
>
>
>
> On Mon, Jan 9, 2023 at 4:28 PM Alistair Francis <alistair23@xxxxxxxxx> wrote:
>>
>> 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
>
>
> Are you referring to the Debug Console Extension (EID #0x4442434E "DBCN")”?
>
> https://lists.riscv.org/g/tech-prs/topic/96051183#84

That's the one!

Alistair

>
> Best,
> Bobby
>
>>
>> >
>> > 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
>> >
>> >