It may happen that the serial IP block is performing some ongoing
transmission (started at e.g. board_init()) when the serial "probe" is
called.
As a result the serial port IP block is reset, so transmitted data is
corrupted:
I2C: ready
DRAM: 1 GiB
jSS('HH��SL_SDHC: 04 rev 0x0
This patch prevents from this situation, by defining pre_probe() callback
in which we wait till the TX buffer is empty (from previous transmission):
I2C: ready
DRAM: 1 GiB
ID: unit type 0x4 rev 0x0
All defined ->pending callbacks at ./drivers/serial are non blocking
- just simple reading from registers and testing flags. Hence, it should
be enough to not use any timeout from timer.
One shall also note that we enable console very early - not all timers
may be ready for work - adding timeout here would impose implicit
dependency that timers are setup before serial.
Signed-off-by: Lukasz Majewski <[email protected]>
---
drivers/serial/serial-uclass.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
index 2e5116f..5e6964d 100644
--- a/drivers/serial/serial-uclass.c
+++ b/drivers/serial/serial-uclass.c
@@ -420,10 +420,30 @@ static int serial_pre_remove(struct udevice *dev)
return 0;
}
+static int serial_pre_probe(struct udevice *dev)
+{
+ struct dm_serial_ops *ops = serial_get_ops(dev);
+ int ret = 0;
+
+ /*
+ * Wait for any ongoing transmission to finish - for example
+ * from pre-relocation enabled UART
+ */
+ if (ops && ops->pending)
+ do {
+ ret = ops->pending(dev, false);
+ if (ret < 0)
+ break;
+ } while (ret > 0);
+
+ return ret;
+}
+
UCLASS_DRIVER(serial) = {
.id = UCLASS_SERIAL,
.name = "serial",
.flags = DM_UC_FLAG_SEQ_ALIAS,
+ .pre_probe = serial_pre_probe,
.post_probe = serial_post_probe,
.pre_remove = serial_pre_remove,
.per_device_auto_alloc_size = sizeof(struct serial_dev_priv),
--
2.1.4
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