powerpc/microwatt: Use standard 16550 UART for console

This adds support to the Microwatt platform to use the standard
16550-style UART which available in the standalone Microwatt FPGA.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/YMwXGCTzedpQje7r@thinks.paulus.ozlabs.org

arch/powerpc/boot/dts/microwatt.dts

@@ -6,6 +6,10 @@ / {
 	model-name = "microwatt";
 	compatible = "microwatt-soc";
 
+	aliases {
+		serial0 = &UART0;
+	};
+
 	reserved-memory {
 		#size-cells = <0x02>;
 		#address-cells = <0x02>;
@@ -89,12 +93,6 @@ PowerPC,Microwatt@0 {
 		};
 	};
 
-	chosen {
-		bootargs = "";
-		ibm,architecture-vec-5 = [19 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00
-					  00 00 00 00 00 00 00 00 40 00 40];
-	};
-
 	soc@c0000000 {
 		compatible = "simple-bus";
 		#address-cells = <1>;
@@ -119,5 +117,22 @@ ICS: interrupt-controller@5000 {
 			#interrupt-cells = <2>;
 		};
 
+		UART0: serial@2000 {
+			device_type = "serial";
+			compatible = "ns16550";
+			reg = <0x2000 0x8>;
+			clock-frequency = <100000000>;
+			current-speed = <115200>;
+			reg-shift = <2>;
+			fifo-size = <16>;
+			interrupts = <0x10 0x1>;
+		};
+	};
+
+	chosen {
+		bootargs = "";
+		ibm,architecture-vec-5 = [19 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00
+					  00 00 00 00 00 00 00 00 40 00 40];
+		stdout-path = &UART0;
 	};
 };

arch/powerpc/kernel/udbg_16550.c

@@ -296,3 +296,42 @@ void __init udbg_init_40x_realmode(void)
 }
 
 #endif /* CONFIG_PPC_EARLY_DEBUG_40x */
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_MICROWATT
+
+#define UDBG_UART_MW_ADDR	((void __iomem *)0xc0002000)
+
+static u8 udbg_uart_in_isa300_rm(unsigned int reg)
+{
+	uint64_t msr = mfmsr();
+	uint8_t  c;
+
+	mtmsr(msr & ~(MSR_EE|MSR_DR));
+	isync();
+	eieio();
+	c = __raw_rm_readb(UDBG_UART_MW_ADDR + (reg << 2));
+	mtmsr(msr);
+	isync();
+	return c;
+}
+
+static void udbg_uart_out_isa300_rm(unsigned int reg, u8 val)
+{
+	uint64_t msr = mfmsr();
+
+	mtmsr(msr & ~(MSR_EE|MSR_DR));
+	isync();
+	eieio();
+	__raw_rm_writeb(val, UDBG_UART_MW_ADDR + (reg << 2));
+	mtmsr(msr);
+	isync();
+}
+
+void __init udbg_init_debug_microwatt(void)
+{
+	udbg_uart_in = udbg_uart_in_isa300_rm;
+	udbg_uart_out = udbg_uart_out_isa300_rm;
+	udbg_use_uart();
+}
+
+#endif /* CONFIG_PPC_EARLY_DEBUG_MICROWATT */

arch/powerpc/platforms/microwatt/Kconfig

@@ -6,6 +6,7 @@ config PPC_MICROWATT
 	select PPC_ICS_NATIVE
 	select PPC_ICP_NATIVE
 	select PPC_NATIVE
+	select PPC_UDBG_16550
 	help
           This option enables support for FPGA-based Microwatt implementations.
 

arch/powerpc/platforms/microwatt/setup.c

@@ -14,6 +14,7 @@
 #include <asm/machdep.h>
 #include <asm/time.h>
 #include <asm/xics.h>
+#include <asm/udbg.h>
 
 static void __init microwatt_init_IRQ(void)
 {
@@ -35,5 +36,6 @@ define_machine(microwatt) {
 	.name			= "microwatt",
 	.probe			= microwatt_probe,
 	.init_IRQ		= microwatt_init_IRQ,
+	.progress		= udbg_progress,
 	.calibrate_decr		= generic_calibrate_decr,
 };