[v5,4/5] xen/riscv: introduce early_printk basic stuff

Commit Message

Oleksii Kurochko Jan. 19, 2023, 2:07 p.m. UTC

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/a3c9916bbdff7ad6030055bbee7e53d1aab71384)
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 <[e-mail]>
Signed-off-by: Oleksii Kurochko <[e-mail]>
Reviewed-by: Bobby Eshleman <[e-mail]>
---
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             | 45 +++++++++++++++++++++++
 xen/arch/riscv/include/asm/early_printk.h | 12 ++++++
 xen/arch/riscv/setup.c                    |  4 ++
 5 files changed, 67 insertions(+)
 create mode 100644 xen/arch/riscv/early_printk.c
 create mode 100644 xen/arch/riscv/include/asm/early_printk.h

Comments

Andrew Cooper Jan. 20, 2023, 12:48 a.m. UTC | #1

On 19/01/2023 2:07 pm, Oleksii Kurochko wrote:
> diff --git a/xen/arch/riscv/early_printk.c b/xen/arch/riscv/early_printk.c
> new file mode 100644
> index 0000000000..6f590e712b
> --- /dev/null
> +++ b/xen/arch/riscv/early_printk.c
> @@ -0,0 +1,45 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * RISC-V early printk using SBI
> + *
> + * Copyright (C) 2021 Bobby Eshleman <[e-mail]>
> + */
> +#include <asm/early_printk.h>
> +#include <asm/sbi.h>
> +
> +/*
> + * 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

This comment is false, and the check is bogus.

It needs deleting.

~Andrew

Julien Grall Jan. 20, 2023, 9:17 a.m. UTC | #2

Hi,

On 20/01/2023 00:48, Andrew Cooper wrote:
> On 19/01/2023 2:07 pm, Oleksii Kurochko wrote:
>> diff --git a/xen/arch/riscv/early_printk.c b/xen/arch/riscv/early_printk.c
>> new file mode 100644
>> index 0000000000..6f590e712b
>> --- /dev/null
>> +++ b/xen/arch/riscv/early_printk.c
>> @@ -0,0 +1,45 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * RISC-V early printk using SBI
>> + *
>> + * Copyright (C) 2021 Bobby Eshleman <[e-mail]>
>> + */
>> +#include <asm/early_printk.h>
>> +#include <asm/sbi.h>
>> +
>> +/*
>> + * 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
> 
> This comment is false, and the check is bogus.

You are already said that in the previous version and ... I reply back 
explaining why I think this is correct (see [1]).

>  > It needs deleting.

That might be the second step. The first step is we settle down on the 
approach.

Cheers,

[1] 
https://lore.kernel.org/xen-devel/[e-mail]/

Patch

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..6f590e712b
--- /dev/null
+++ b/xen/arch/riscv/early_printk.c
@@ -0,0 +1,45 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * RISC-V early printk using SBI
+ *
+ * Copyright (C) 2021 Bobby Eshleman <[e-mail]>
+ */
+#include <asm/early_printk.h>
+#include <asm/sbi.h>
+
+/*
+ * 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
+
+/*
+ * 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");