From: Alistair Francis <alistair23@gmail.com>
To: Oleksii <oleksii.kurochko@gmail.com>
Cc: xen-devel@lists.xenproject.org,
Bob Eshleman <bobbyeshleman@gmail.com>,
Alistair Francis <alistair.francis@wdc.com>,
Julien Grall <julien@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Jan Beulich <jbeulich@suse.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Gianluca Guida <gianluca@rivosinc.com>,
Connor Davis <connojdavis@gmail.com>,
Bobby Eshleman <bobby.eshleman@gmail.com>
Subject: Re: [PATCH v7 1/2] xen/riscv: introduce early_printk basic stuff
Date: Tue, 31 Jan 2023 21:44:33 +1000 [thread overview]
Message-ID: <CAKmqyKMGiDiPRZBekdKan=+YduSmkB2DoWo5btrtVQ8nS3KMAg@mail.gmail.com> (raw)
In-Reply-To: <f5cd1bfb116bfcc86fc2848df7eead05cd1a24c0.camel@gmail.com>
On Sat, Jan 28, 2023 at 12:15 AM Oleksii <oleksii.kurochko@gmail.com> wrote:
>
> Hi Alistair, Bobby and community,
>
> I would like to ask your help with the following check:
> +/*
> + * early_*() can be called from head.S with MMU-off.
> + *
> + * The following requiremets should be honoured for early_*() to
> + * work correctly:
> + * It should use PC-relative addressing for accessing symbols.
> + * To achieve that GCC cmodel=medany should be used.
> + */
> +#ifndef __riscv_cmodel_medany
> +#error "early_*() can be called from head.S with MMU-off"
> +#endif
I have never seen a check like this before. I don't really understand
what it's looking for, if the linker is unable to call early_*() I
would expect it to throw an error. I'm not sure what this is adding.
I think this is safe to remove.
Alistair
>
> Please take a look at the following messages and help me to decide if
> the check mentioned above should be in early_printk.c or not:
> [1]
> https://lore.kernel.org/xen-devel/599792fa-b08c-0b1e-10c1-0451519d9e4a@xen.org/
> [2]
> https://lore.kernel.org/xen-devel/0ec33871-96fa-bd9f-eb1b-eb37d3d7c982@xen.org/
>
> Thanks in advance.
>
> ~ Oleksii
>
> On Fri, 2023-01-27 at 13:39 +0200, Oleksii Kurochko wrote:
> > 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.
> >
> > The patch introduces the basic stuff of early_printk functionality
> > which will be enough to print 'hello from C environment".
> >
> > Originally early_printk.{c,h} was introduced by Bobby Eshleman
> > (
> > https://github.com/glg-rv/xen/commit/a3c9916bbdff7ad6030055bbee7e53d1a
> > ab71384)
> > but some functionality was changed:
> > early_printk() function was changed in comparison with the original
> > as
> > common isn't being built now so there is no vscnprintf.
> >
> > This commit adds early printk implementation built on the putc SBI
> > call.
> >
> > As sbi_console_putchar() is already being planned for deprecation
> > it is used temporarily now and will be removed or reworked after
> > real uart will be ready.
> >
> > Signed-off-by: Bobby Eshleman <bobby.eshleman@gmail.com>
> > Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> > Reviewed-by: Bobby Eshleman <bobby.eshleman@gmail.com>
> > ---
> > Changes in V7:
> > - Nothing was changed
> > ---
> > Changes in V6:
> > - Remove __riscv_cmodel_medany check from early_printk.c
> > ---
> > Changes in V5:
> > - Code style fixes
> > - Change an error message of #error in case of
> > __riscv_cmodel_medany
> > isn't defined
> > ---
> > Changes in V4:
> > - Remove "depends on RISCV*" from Kconfig.debug as it is located
> > in
> > arch specific folder so by default RISCV configs should be
> > ebabled.
> > - Add "ifdef __riscv_cmodel_medany" to be sure that PC-relative
> > addressing
> > is used as early_*() functions can be called from head.S with
> > MMU-off and
> > before relocation (if it would be needed at all for RISC-V)
> > - fix code style
> > ---
> > Changes in V3:
> > - reorder headers in alphabetical order
> > - merge changes related to start_xen() function from "[PATCH v2
> > 7/8]
> > xen/riscv: print hello message from C env" to this patch
> > - remove unneeded parentheses in definition of STACK_SIZE
> > ---
> > Changes in V2:
> > - introduce STACK_SIZE define.
> > - use consistent padding between instruction mnemonic and
> > operand(s)
> > ---
> > xen/arch/riscv/Kconfig.debug | 5 ++++
> > xen/arch/riscv/Makefile | 1 +
> > xen/arch/riscv/early_printk.c | 33
> > +++++++++++++++++++++++
> > xen/arch/riscv/include/asm/early_printk.h | 12 +++++++++
> > xen/arch/riscv/setup.c | 4 +++
> > 5 files changed, 55 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..608c9ff832 100644
> > --- a/xen/arch/riscv/Kconfig.debug
> > +++ b/xen/arch/riscv/Kconfig.debug
> > @@ -0,0 +1,5 @@
> > +config EARLY_PRINTK
> > + bool "Enable early printk"
> > + default DEBUG
> > + 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..b66a11f1bc
> > --- /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/early_printk.h>
> > +#include <asm/sbi.h>
> > +
> > +/*
> > + * TODO:
> > + * sbi_console_putchar is already planned for deprecation
> > + * 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__ */
> > diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
> > index 13e24e2fe1..d09ffe1454 100644
> > --- a/xen/arch/riscv/setup.c
> > +++ b/xen/arch/riscv/setup.c
> > @@ -1,12 +1,16 @@
> > #include <xen/compile.h>
> > #include <xen/init.h>
> >
> > +#include <asm/early_printk.h>
> > +
> > /* Xen stack for bringing up the first CPU. */
> > unsigned char __initdata cpu0_boot_stack[STACK_SIZE]
> > __aligned(STACK_SIZE);
> >
> > void __init noreturn start_xen(void)
> > {
> > + early_printk("Hello from C env\n");
> > +
> > for ( ;; )
> > asm volatile ("wfi");
> >
>
>
next prev parent reply other threads:[~2023-01-31 11:45 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-27 11:39 [PATCH v7 0/2] Basic early_printk and smoke test implementation Oleksii Kurochko
2023-01-27 11:39 ` [PATCH v7 1/2] xen/riscv: introduce early_printk basic stuff Oleksii Kurochko
2023-01-27 14:15 ` Oleksii
2023-01-31 11:44 ` Alistair Francis [this message]
2023-01-31 12:03 ` Julien Grall
2023-01-31 23:17 ` Alistair Francis
2023-02-01 0:21 ` Andrew Cooper
2023-02-01 9:06 ` Julien Grall
2023-02-01 9:10 ` Julien Grall
2023-02-01 17:33 ` Bobby Eshleman
2023-02-04 11:59 ` Alistair Francis
2023-02-06 17:30 ` Oleksii
2023-01-27 11:39 ` [PATCH v7 2/2] automation: add RISC-V smoke test Oleksii Kurochko
2023-01-27 18:14 ` Stefano Stabellini
2023-01-31 11:21 ` Oleksii
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