From: "Neil Armstrong" <neil.armstrong@linaro.org>
To: Mattijs Korpershoek <mkorpershoek@baylibre.com>,
u-boot-amlogic@groups.io
Cc: u-boot@lists.denx.de
Subject: Re: [PATCH] serial: meson: fix meson_serial_pending() tx logic
Date: Wed, 7 Jun 2023 10:03:19 +0200 [thread overview]
Message-ID: <5699d7cb-0861-a21a-2928-eb2e7e80f63d@linaro.org> (raw)
In-Reply-To: <20230606-fix-meson-serial-pending-v1-1-6a54d4a01f76@baylibre.com>
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>
prev parent reply other threads:[~2023-06-07 8:03 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-06 16:07 [PATCH] serial: meson: fix meson_serial_pending() tx logic Mattijs Korpershoek
2023-06-07 8:03 ` Neil Armstrong [this message]
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