xen/riscv: introduce early_printk basic stuff

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 <bobby.eshleman@gmail.com>
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Bobby Eshleman <bobby.eshleman@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

diff --git a/xen/arch/riscv/Kconfig.debug b/xen/arch/riscv/Kconfig.debug
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..608c9ff832bcf09307e9a5ef8ac43741995a58a3 100644 (file)
--- 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 fd916e1004c34eca751f920d35378ef259b86d78..1a4f1a6015a61e0b1972c7fb10e481160514e709 100644 (file)
--- 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 (file)
index 0000000..dfe4ad7
--- /dev/null
+++ b/xen/arch/riscv/early_printk.c
@@ -0,0 +1,44 @@
+/* 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>
+
+/*
+ * When the MMU is off during early boot, any C function called has to
+ * use PC-relative rather than absolute address because the physical address
+ * may not match the virtual address.
+ *
+ * To guarantee PC-relative address 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 (file)
index 0000000..05106e1
--- /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 13e24e2fe1a38a5cebd6b5bc2ce706523db68957..d09ffe1454a4f1f262dc8ac2d96b53156b8d2a71 100644 (file)
--- 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");