From afa85a2247297d660a63295bfbdd6e24e8e56902 Mon Sep 17 00:00:00 2001
From: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Date: Tue, 6 Jun 2023 18:07:48 +0200
Subject: [PATCH] serial: meson: fix meson_serial_pending() tx logic
According to the dm_serial_ops documentation, pending() should:
> @return number of waiting characters, 0 for none, -ve on error
And:
> It is acceptable to return 1 if an indeterminant number
> of characters is waiting.
With the current implementation, we have:
* FIFO is full -> pending() returns 0
* FIFO is partially used -> pending() returns 1
* FIFO is empty -> pending() returns 1
This is not the same as what the documentation requires.
Moreover, since [1], arm reset now flushes all console devices
(including serial) before the cpu gets reset.
Because of the flawed logic:
=> reset # user calls reset
flush() is called
_serial_flush() is called
ops->pending(dev, false) # never returns false
# board hangs indefinitely without resetting.
Fix it by using AML_UART_TX_EMPTY instead of AML_UART_TX_FULL.
[1] commit c5f4cdb8eb60 ("console: Use flush() before panic and reset"),
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230606-fix-meson-serial-pending-v1-1-6a54d4a01f76@baylibre.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
---
drivers/serial/serial_meson.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/serial/serial_meson.c b/drivers/serial/serial_meson.c
index d026f5a7a8..934de2ab23 100644
--- a/drivers/serial/serial_meson.c
+++ b/drivers/serial/serial_meson.c
@@ -201,7 +201,10 @@ static int meson_serial_pending(struct udevice *dev, bool input)
return true;
} else {
- return !(status & AML_UART_TX_FULL);
+ if (status & AML_UART_TX_EMPTY)
+ return false;
+
+ return true;
}
}
--
2.39.5