hello_world: Use ldcix/stdcix to access UART

This is one step towards ultimately removing the address-based
cache inhibit hack from dcache.vhdl.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

hello_world/console.c

@@ -25,23 +25,16 @@ static uint64_t potato_uart_base;
 
 static uint64_t potato_uart_reg_read(int offset)
 {
-	uint64_t addr;
 	uint64_t val;
 
-	addr = potato_uart_base + offset;
-
-	val = *(volatile uint64_t *)addr;
+	__asm__ volatile("ldcix %0,%1,%2" : "=r" (val) : "b" (potato_uart_base), "r" (offset));
 
 	return val;
 }
 
 static void potato_uart_reg_write(int offset, uint64_t val)
 {
-	uint64_t addr;
-
-	addr = potato_uart_base + offset;
-
-	*(volatile uint64_t *)addr = val;
+	__asm__ volatile("stdcix %0,%1,%2" : : "r" (val), "b" (potato_uart_base), "r" (offset));
 }
 
 static int potato_uart_rx_empty(void)

hello_world/hello_world.hex

@@ -40,7 +40,7 @@ a64b5a7d14004a39
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 0000000000000000
 0000000000000000
@@ -513,74 +513,55 @@ a64b5a7d14004a39
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 0000000000000000
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 0000000000000000
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