[PATCH v2 6/9] MIPS: debug_ll: Implement support for Alchemy uarts

[Jiaxun Yang]

Alchemy uart is a 8250 derivative that requires some special care
on barriers and readys, also they have a wired register layout.

Implement it as a special include.

Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
---
 arch/mips/Kconfig.debug           | 10 +++++++++
 arch/mips/include/debug/alchemy.S | 46 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 3609d298a9eb..aef116058654 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -257,11 +257,20 @@ choice
 		  Say Y here if you want kernel low-level debugging support
 		  on uart0 of Ingenic SoCs.
 
+	config DEBUG_ALCHEMY_UART
+		bool "Kernel low-level debugging messages via Alchemy UART"
+		depends on MIPS_ALCHEMY
+		select DEBUG_LL_UART
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on uart of alchemy SoCs.
+
 endchoice
 
 config DEBUG_LL_INCLUDE
 	string
 	default "debug/8250.S" if DEBUG_LL_UART_8250 || DEBUG_UART_8250
+	default "debug/alchemy.S" if DEBUG_ALCHEMY_UART
 	default "debug/uhi.S" if DEBUG_MIPS_UHI
 	default "debug-macro.S"
 
@@ -293,6 +302,7 @@ config DEBUG_UART_PHYS
 	default 0x1fd003f8 if DEBUG_LOONGSON3_UART
 	default 0x1fe00000 if DEBUG_LOONGSON2K_UART
 	default 0x10030000 if DEBUG_INGENIC_UART
+	default 0x11100000 if DEBUG_ALCHEMY_UART
 	help
 	  This is the physical base address of the debug UART. It must be
 	  accessible from unmapped kernel space (i.e. KSEG1 for 32bit kernels
diff --git a/arch/mips/include/debug/alchemy.S b/arch/mips/include/debug/alchemy.S
new file mode 100644
index 000000000000..933efc6e828c
--- /dev/null
+++ b/arch/mips/include/debug/alchemy.S
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
+ * MIPS Low level debug include file for Au1xxx UART
+ * Dereived from drivers/tty/serial/8250/8250_rt288x.c
+ */
+
+#include <asm/addrspace.h>
+#include <asm/asm.h>
+#include <linux/serial_reg.h>
+
+#define DEBUG_LL_UART
+
+#define UART_BASE	CKSEG1ADDR(CONFIG_DEBUG_UART_PHYS)
+
+#define UART_TX_OFS	(1 << 2)
+#define UART_LSR_OFS	(7 << 2)
+
+# define UART_L		lw
+# define UART_S		sw
+
+		.macro	addruart,rd,rx
+		PTR_LA	\rd, UART_BASE
+		.endm
+
+		.macro	senduart,rd,rx
+		UART_S   \rd, UART_TX_OFS(\rx)
+		sync	/* wmb */
+		.endm
+
+		.macro	busyuart,rd,rx
+1002:
+		UART_L	\rd, UART_LSR_OFS(\rx)
+		andi	\rd, \rd, (UART_LSR_TEMT | UART_LSR_THRE)
+		xori	\rd, (UART_LSR_TEMT | UART_LSR_THRE)
+		sync	/* cpu_relax */
+		bnez	\rd, 1002b
+		.endm
+
+		.macro	waituarttxrdy,rd,rx
+		busyuart \rd, \rx
+		.endm
+
+		/* Au1xxx has no MSR */
+		.macro	waituartcts,rd,rx
+		.endm

-- 
2.34.1