From afa85a2247297d660a63295bfbdd6e24e8e56902 Mon Sep 17 00:00:00 2001 From: Mattijs Korpershoek Date: Tue, 6 Jun 2023 18:07:48 +0200 Subject: 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 Acked-by: Neil Armstrong Link: https://lore.kernel.org/r/20230606-fix-meson-serial-pending-v1-1-6a54d4a01f76@baylibre.com Signed-off-by: Neil Armstrong --- 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 d026f5a7a8e5..934de2ab2358 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; } } -- cgit v1.2.3