[U-Boot] [PATCH 2/2] serial: bcm283x_mu: Detect disabled serial device

[Alexander Graf <agraf@suse.de>]

On the raspberry pi, you can disable the serial port to gain dynamic frequency
scaling which can get handy at times.

However, in such a configuration the serial controller gets its rx queue filled
up with zero bytes which then happily get transmitted on to whoever calls
getc() today.

This patch adds detection logic for that case by checking whether the RX pin is
mapped to GPIO15 and disables the mini uart if it is not mapped properly.

That way we can leave the driver enabled in the tree and can determine during
runtime whether serial is usable or not, having a single binary that allows for
uart and non-uart operation.

Signed-off-by: Alexander Graf <agraf@suse.de>

---

v2 -> v3:

  - Disable and detect pinmux in board file
---
 board/raspberrypi/rpi/rpi.c | 29 +++++++++++++++++++++++++++++
 configs/rpi_3_32b_defconfig |  1 +
 configs/rpi_3_defconfig     |  1 +
 include/configs/rpi.h       |  1 +
 4 files changed, 32 insertions(+)

diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index 4c8253d..20b0d1b 100644
--- a/board/raspberrypi/rpi/rpi.c
+++ b/board/raspberrypi/rpi/rpi.c
@@ -453,6 +453,35 @@ int board_init(void)
 	return power_on_module(BCM2835_MBOX_POWER_DEVID_USB_HCD);
 }
 
+static bool rpi_is_serial_active(void)
+{
+#ifndef CONFIG_PL01X_SERIAL
+	int serial_gpio = 15;
+	struct udevice *dev;
+
+	/*
+	 * The RPi3 disables the mini uart by default. The easiest way to find
+	 * out whether it is available is to check if the pin is muxed.
+	 */
+	if (uclass_first_device(UCLASS_GPIO, &dev) || !dev)
+		return true;
+
+	if (bcm2835_gpio_get_func_id(dev, serial_gpio) != BCM2835_GPIO_ALT5)
+		return false;
+#endif
+
+	return true;
+}
+
+int board_late_init(void)
+{
+	/* Disable mini-UART I/O if it's not pinmuxed to our pins */
+	if (!rpi_is_serial_active())
+		gd->cur_serial_dev = NULL;
+
+	return 0;
+}
+
 int board_mmc_init(bd_t *bis)
 {
 	ALLOC_CACHE_ALIGN_BUFFER(struct msg_get_clock_rate, msg_clk, 1);
diff --git a/configs/rpi_3_32b_defconfig b/configs/rpi_3_32b_defconfig
index 922e01b..4c2f106 100644
--- a/configs/rpi_3_32b_defconfig
+++ b/configs/rpi_3_32b_defconfig
@@ -20,3 +20,4 @@ CONFIG_CMD_FAT=y
 CONFIG_CMD_FS_GENERIC=y
 CONFIG_PHYS_TO_BUS=y
 CONFIG_OF_LIBFDT=y
+# CONFIG_REQUIRE_SERIAL_CONSOLE is not set
diff --git a/configs/rpi_3_defconfig b/configs/rpi_3_defconfig
index bff92df..288214c 100644
--- a/configs/rpi_3_defconfig
+++ b/configs/rpi_3_defconfig
@@ -19,3 +19,4 @@ CONFIG_CMD_FAT=y
 CONFIG_CMD_FS_GENERIC=y
 CONFIG_PHYS_TO_BUS=y
 CONFIG_OF_LIBFDT=y
+# CONFIG_REQUIRE_SERIAL_CONSOLE is not set
diff --git a/include/configs/rpi.h b/include/configs/rpi.h
index b5543f4..e3b890a 100644
--- a/include/configs/rpi.h
+++ b/include/configs/rpi.h
@@ -22,6 +22,7 @@
 
 /* Architecture, CPU, etc.*/
 #define CONFIG_ARCH_CPU_INIT
+#define CONFIG_BOARD_LATE_INIT
 
 /* Use SoC timer for AArch32, but architected timer for AArch64 */
 #ifndef CONFIG_ARM64
-- 
1.8.5.6