[xen master] xen/riscv: introduce early_printk basic stuff

[patchbot@xxxxxxx]

commit 46a78347e2f6706b192eaf5992fec5c3cfe885ae
Author:     Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Thu Feb 9 11:13:50 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 9 11:13:50 2023 +0100

    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@xxxxxxxxx>
    Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    Reviewed-by: Bobby Eshleman <bobby.eshleman@xxxxxxxxx>
    Reviewed-by: Alistair Francis <alistair.francis@xxxxxxx>
---
 xen/arch/riscv/Kconfig.debug              |  5 ++++
 xen/arch/riscv/Makefile                   |  1 +
 xen/arch/riscv/early_printk.c             | 44 +++++++++++++++++++++++++++++++
 xen/arch/riscv/include/asm/early_printk.h | 12 +++++++++
 xen/arch/riscv/setup.c                    |  4 +++
 5 files changed, 66 insertions(+)

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..dfe4ad77e2
--- /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@xxxxxxxxx>
+ */
+#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
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");
 
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