powerpc/uart: Choose which UART to use at build time, not runtime.

Microwatt may have firmware that places data in r3, which was used to
detect microwatt vs powernv.  This breaks the existing probing of the UART
type in this powerpc port.

Instead build only the appropriate UART into the firmware, selected by
passing the option UART=potato or UART=lpc_serial to the Makefile.

A future enhancement would be to parse the device tree and configure
MicroPython based on the settings.

Author: shenki

ports/powerpc/Makefile

@@ -6,6 +6,9 @@ QSTR_DEFS = qstrdefsport.h
 # include py core make definitions
 include $(TOP)/py/py.mk
 
+# potato or lpc_serial
+UART ?= potato
+
 ARCH = $(shell uname -m)
 ifneq ("$(ARCH)", "ppc64")
 ifneq ("$(ARCH)", "ppc64le")
@@ -30,9 +33,7 @@ LIBS =
 
 SRC_C = \
 	main.c \
-	uart_core.c \
-	uart_potato.c \
-	uart_lpc_serial.c \
+	uart_$(UART).c \
 	lib/utils/printf.c \
 	lib/utils/stdout_helpers.c \
 	lib/utils/pyexec.c \

ports/powerpc/README.md

@@ -6,10 +6,14 @@ potato UART.
 
 ## Building
 
-By default the port will be built for the host machine:
+By default the port will be built with the potato uart for microwatt:
 
     $ make
 
+To instead build for a machine with LPC serial, such as QEMU powernv:
+
+    $ make UART=lpc_serial
+
 ## Cross compilation for POWERPC
 
 If you need to cross compilers you'll want to grab a powerpc64le

ports/powerpc/main.c

@@ -65,7 +65,6 @@ int main(int argc, char **argv) {
     int stack_dummy;
     stack_top = (char *)&stack_dummy;
 
-    // microwatt has argc/r3 = 0 whereas QEMU has r3 set in head.S
     uart_init_ppc(argc);
 
     #if MICROPY_ENABLE_PYSTACK

ports/powerpc/uart_core.c

@@ -96,20 +96,24 @@ static int lpc_uart_rx_empty(void) {
     return !(lpc_uart_reg_read(REG_LSR) & LSR_DR);
 }
 
-void lpc_uart_init(void) {
+void uart_init_ppc(void) {
     lpc_uart_base = LPC_UART_BASE;
 }
 
-char lpc_uart_read(void) {
+int mp_hal_stdin_rx_chr(void) {
     while (lpc_uart_rx_empty()) {
         ;
     }
     return lpc_uart_reg_read(REG_THR);
 }
 
-void lpc_uart_write(char c) {
-    while (lpc_uart_tx_full()) {
-        ;
+
+void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    int i;
+    for (i = 0; i < len; i++) {
+        while (lpc_uart_tx_full()) {
+            ;
+        }
+        lpc_uart_reg_write(REG_RBR, str[i]);
     }
-    lpc_uart_reg_write(REG_RBR, c);
 }

ports/powerpc/uart_lpc_serial.c

@@ -34,10 +34,12 @@
 #include <stdbool.h>
 #include "py/mpconfig.h"
 
-#define PROC_FREQ                           50000000
+#define SYSCON_BASE     0xc0000000  /* System control regs */
+#define SYS_REG_CLKINFO                 0x20
+
 #define UART_FREQ                           115200
 #define POTATO_UART_BASE                    0xc0002000
-uint64_t potato_uart_base;
+static uint64_t potato_uart_base;
 
 #define POTATO_CONSOLE_TX                   0x00
 #define POTATO_CONSOLE_RX                   0x08
@@ -60,7 +62,7 @@ static uint64_t potato_uart_reg_read(int offset) {
     return val;
 }
 
-void potato_uart_reg_write(int offset, uint64_t val) {
+static void potato_uart_reg_write(int offset, uint64_t val) {
     uint64_t addr;
 
     addr = potato_uart_base + offset;
@@ -96,13 +98,16 @@ static unsigned long potato_uart_divisor(unsigned long proc_freq, unsigned long
     return proc_freq / (uart_freq * 16) - 1;
 }
 
-void potato_uart_init(void) {
+void uart_init_ppc(void) {
+    uint64_t proc_freq;
+
     potato_uart_base = POTATO_UART_BASE;
-    potato_uart_reg_write(POTATO_CONSOLE_CLOCK_DIV, potato_uart_divisor(PROC_FREQ, UART_FREQ));
+    proc_freq = *(volatile uint64_t *)(SYSCON_BASE + SYS_REG_CLKINFO);
+    potato_uart_reg_write(POTATO_CONSOLE_CLOCK_DIV, potato_uart_divisor(proc_freq, UART_FREQ));
 
 }
 
-char potato_uart_read(void) {
+int mp_hal_stdin_rx_chr(void) {
     uint64_t val;
 
     while (potato_uart_rx_empty()) {
@@ -113,13 +118,15 @@ char potato_uart_read(void) {
     return (char)(val & 0x000000ff);
 }
 
-void potato_uart_write(char c) {
-    uint64_t val;
+void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    int i;
 
-    val = c;
+    for (i = 0; i < len; i++) {
+        uint64_t val = str[i];
 
-    while (potato_uart_tx_full()) {
-        ;
+        while (potato_uart_tx_full()) {
+            ;
+        }
+        potato_uart_reg_write(POTATO_CONSOLE_TX, val);
     }
-    potato_uart_reg_write(POTATO_CONSOLE_TX, val);
 }