[PATCH 3/9] RISC-V: virt: riscvemu: add HTIF DEBUG_LL support

[Ahmad Fatoum]

Default console of riscvemu is available Virt I/O console and as a HTIF
blocking character device. We already support Virt I/O console, but the
HTIF is easier to support for very early low level debugging. Add
DEBUG_LL support to facilitate using it.

Note: when using a framebuffer, riscvemu doesn't allocate a default
console, so barebox calling into HTIF will segfault the emulator.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 arch/riscv/include/asm/debug_ll.h | 11 +++++++++++
 arch/riscv/include/asm/htif.h     |  9 +++++++++
 common/Kconfig                    |  9 +++++++++
 3 files changed, 29 insertions(+)

diff --git a/arch/riscv/include/asm/debug_ll.h b/arch/riscv/include/asm/debug_ll.h
index 867c96d79724..de9bc5f5fd33 100644
--- a/arch/riscv/include/asm/debug_ll.h
+++ b/arch/riscv/include/asm/debug_ll.h
@@ -53,6 +53,17 @@ static inline void PUTC_LL(char ch)
 
 #include <asm/debug_ll_litex.h>
 
+#elif defined CONFIG_DEBUG_RISCVEMU_HTIF
+
+#include <asm/htif.h>
+
+#ifndef __ASSEMBLY__
+static inline void PUTC_LL(char ch)
+{
+	htif_putc(IOMEM(HTIF_DEFAULT_BASE_ADDR), ch);
+}
+#endif
+
 #endif
 
 #ifndef debug_ll_init
diff --git a/arch/riscv/include/asm/htif.h b/arch/riscv/include/asm/htif.h
index 7312f09d2e6e..b35afdd98e1d 100644
--- a/arch/riscv/include/asm/htif.h
+++ b/arch/riscv/include/asm/htif.h
@@ -11,6 +11,10 @@
 #define HTIF_DEV_SYSCALL		0
 #define		HTIF_CMD_SYSCALL	0
 
+#define HTIF_DEV_CONSOLE		1 /* blocking character device */
+#define		HTIF_CMD_GETCHAR	0
+#define		HTIF_CMD_PUTCHAR	1
+
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>
@@ -26,6 +30,11 @@ static inline void htif_tohost(u8 device, u8 command, u64 arg)
 	__htif_tohost(IOMEM(HTIF_DEFAULT_BASE_ADDR), device, command, arg);
 }
 
+static inline void htif_putc(void __iomem *base, int c)
+{
+	__htif_tohost(base, HTIF_DEV_CONSOLE, HTIF_CMD_PUTCHAR, c);
+}
+
 #endif
 
 #endif
diff --git a/common/Kconfig b/common/Kconfig
index 802bd9bfbb2e..2f014509da0d 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -1403,6 +1403,15 @@ config DEBUG_RISCV_VIRT
 	depends on SOC_VIRT
 	select DEBUG_LL_NS16550
 
+config DEBUG_RISCVEMU_HTIF
+	bool "riscvemu HTIF port"
+	depends on SOC_VIRT
+	help
+	  When run without graphics support, tinyemu will expose access
+	  to the Virt I/O console as HTIF blocking console device as well.
+	  This is useful for low level debugging before Virt I/O DMA is
+	  initialized.
+
 config DEBUG_SIFIVE
 	bool "SiFive serial0 port"
 	depends on SOC_SIFIVE
-- 
2.30.2