[kvm-unit-tests PATCH] lib/arm/io: Fix calling getchar() multiple times

[Thomas Huth <thuth@redhat.com>]

getchar() can currently only be called once on arm since the implementation
is a little bit too  naïve: After the first character has arrived, the
data register never gets set to zero again. To properly check whether a
byte is available, we need to check the "RX fifo empty" on the pl011 UART
or the "RX data ready" bit on the ns16550a UART instead.

With this proper check in place, we can finally also get rid of the
ugly assert(count < 16) statement here.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 lib/arm/io.c | 34 ++++++++++++++--------------------
 1 file changed, 14 insertions(+), 20 deletions(-)

diff --git a/lib/arm/io.c b/lib/arm/io.c
index c15e57c4..836fa854 100644
--- a/lib/arm/io.c
+++ b/lib/arm/io.c
@@ -28,6 +28,7 @@ static struct spinlock uart_lock;
  */
 #define UART_EARLY_BASE (u8 *)(unsigned long)CONFIG_UART_EARLY_BASE
 static volatile u8 *uart0_base = UART_EARLY_BASE;
+bool is_pl011_uart;
 
 static void uart0_init_fdt(void)
 {
@@ -59,7 +60,10 @@ static void uart0_init_fdt(void)
 			abort();
 		}
 
+		is_pl011_uart = (i == 0);
 	} else {
+		is_pl011_uart = !fdt_node_check_compatible(dt_fdt(), ret,
+		                                           "arm,pl011");
 		ret = dt_pbus_translate_node(ret, 0, &base);
 		assert(ret == 0);
 	}
@@ -111,31 +115,21 @@ void puts(const char *s)
 	spin_unlock(&uart_lock);
 }
 
-static int do_getchar(void)
+int __getchar(void)
 {
-	int c;
+	int c = -1;
 
 	spin_lock(&uart_lock);
-	c = readb(uart0_base);
-	spin_unlock(&uart_lock);
-
-	return c ?: -1;
-}
-
-/*
- * Minimalist implementation for migration completion detection.
- * Without FIFOs enabled on the QEMU UART device we just read
- * the data register: we cannot read more than 16 characters.
- */
-int __getchar(void)
-{
-	int c = do_getchar();
-	static int count;
 
-	if (c != -1)
-		++count;
+	if (is_pl011_uart) {
+		if (!(readb(uart0_base + 6 * 4) & 0x10))  /* RX not empty? */
+			c = readb(uart0_base);
+	} else {
+		if (readb(uart0_base + 5) & 0x01)         /* RX data ready? */
+			c = readb(uart0_base);
+	}
 
-	assert(count < 16);
+	spin_unlock(&uart_lock);
 
 	return c;
 }
-- 
2.43.0