[U-Boot] [PATCH v2 2/7] serial: Allow boards to determine whether a serial device is usable

[Alexander Graf <agraf@suse.de>]

On some boards, serial devices may or may not be muxed properly to actual
pins, depending on firmware configuration. To determine whether we should
use a serial device for U-Boot in-/output, we need to check whether it
is muxed properly.

This is something only the board file can do, so let's expose a weak
function that a board can override to explicitly allow or disallow
usage of certain serial devices.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 drivers/serial/serial-uclass.c | 11 +++++++++++
 include/serial.h               | 11 +++++++++++
 2 files changed, 22 insertions(+)

diff --git a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
index 68ca2d09d1..ecd64f8e86 100644
--- a/drivers/serial/serial-uclass.c
+++ b/drivers/serial/serial-uclass.c
@@ -366,6 +366,16 @@ static int on_baudrate(const char *name, const char *value, enum env_op op,
 U_BOOT_ENV_CALLBACK(baudrate, on_baudrate);
 
 #if CONFIG_IS_ENABLED(SERIAL_PRESENT)
+__weak int board_check_serial(struct udevice *dev)
+{
+	return 0;
+}
+
+static int serial_pre_probe(struct udevice *dev)
+{
+	return board_check_serial(dev);
+}
+
 static int serial_post_probe(struct udevice *dev)
 {
 	struct dm_serial_ops *ops = serial_get_ops(dev);
@@ -438,6 +448,7 @@ UCLASS_DRIVER(serial) = {
 	.name		= "serial",
 	.flags		= DM_UC_FLAG_SEQ_ALIAS,
 	.post_probe	= serial_post_probe,
+	.pre_probe	= serial_pre_probe,
 	.pre_remove	= serial_pre_remove,
 	.per_device_auto_alloc_size = sizeof(struct serial_dev_priv),
 };
diff --git a/include/serial.h b/include/serial.h
index d87f01082a..221b3e1402 100644
--- a/include/serial.h
+++ b/include/serial.h
@@ -207,4 +207,15 @@ void sh_serial_initialize(void);
 void uartlite_serial_initialize(void);
 void zynq_serial_initialize(void);
 
+/**
+ * board_check_serial() - Determine whether a serial device works
+ *
+ * This is a board callback that allows boards to override whether a serial
+ * device is usable. By default, all devices are declared usable.
+ *
+ * @dev: Device pointer
+ * @return 0 if the device is usable, !0 otherwise
+ */
+int board_check_serial(struct udevice *dev);
+
 #endif
-- 
2.12.3