* [PATCH] serial: meson: fix meson_serial_pending() tx logic
@ 2023-06-06 16:07 Mattijs Korpershoek
2023-06-07 8:03 ` Neil Armstrong
0 siblings, 1 reply; 2+ messages in thread
From: Mattijs Korpershoek @ 2023-06-06 16:07 UTC (permalink / raw)
To: Neil Armstrong, u-boot-amlogic; +Cc: u-boot, Mattijs Korpershoek
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>
---
Tested with:
=> reset # vim3 board no longer hangs
---
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;
}
}
---
base-commit: a1fd9cb41fb1fda2283a089f9c97e5eed4d4940a
change-id: 20230606-fix-meson-serial-pending-890e11467215
Best regards,
--
Mattijs Korpershoek <mkorpershoek@baylibre.com>
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] serial: meson: fix meson_serial_pending() tx logic
2023-06-06 16:07 [PATCH] serial: meson: fix meson_serial_pending() tx logic Mattijs Korpershoek
@ 2023-06-07 8:03 ` Neil Armstrong
0 siblings, 0 replies; 2+ messages in thread
From: Neil Armstrong @ 2023-06-07 8:03 UTC (permalink / raw)
To: Mattijs Korpershoek, u-boot-amlogic; +Cc: u-boot
On 06/06/2023 18:07, Mattijs Korpershoek wrote:
> 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>
> ---
> Tested with:
> => reset # vim3 board no longer hangs
> ---
> 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;
> }
> }
>
>
> ---
> base-commit: a1fd9cb41fb1fda2283a089f9c97e5eed4d4940a
> change-id: 20230606-fix-meson-serial-pending-890e11467215
>
> Best regards,
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2023-06-06 16:07 [PATCH] serial: meson: fix meson_serial_pending() tx logic Mattijs Korpershoek
2023-06-07 8:03 ` Neil Armstrong
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