Re: [PATCH 1/2] serial: 8250: Add RX trigger levels for U6_16550A

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found no new issues
in this patch, but noticed 1 related pre-existing issue it does not
introduce:
- [Medium] serial: 8250: unpopulated rxtrig_bytes states in
  bytes_to_fcr_rxtrig() [1]
--

commit a186be2f155b931d20413d24643c82a17676db0e
Author: Kryštof Černý <cleverline1mc@gmail.com>

serial: 8250: Add RX trigger levels for U6_16550A

This commit populates the rxtrig_bytes table for PORT_U6_16550A in
uart_config[] so that the rx_trig_bytes sysfs attribute is exposed for
ports of this type.

> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 36b2b0a2c05cd..a7acede62f40f 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -163,6 +163,7 @@ static const struct serial8250_config uart_config[] = {
>  		.fifo_size	= 64,
>  		.tx_loadsz	= 64,
>  		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10,
> +		.rxtrig_bytes	= {1, 16, 32, 62},
>  		.flags		= UART_CAP_FIFO | UART_CAP_AFE,
>  	},
>  	[PORT_TEGRA] = {

[Severity: Medium]
This problem wasn't introduced by this patch, but in the same
uart_config[] table, can writing a value of 4 or greater to rx_trig_bytes
on UART_PORT_AIROHA_HS select an unpopulated trigger state [1]?

drivers/tty/serial/8250/8250_port.c:
	[UART_PORT_AIROHA_HS] = {
		...
		.rxtrig_bytes	= {1, 4},
		.flags		= UART_CAP_FIFO,
	},

Because rxtrig_bytes only initializes the first two entries (unlike
UART_PORT_AIROHA, which uses {1, 4, 4, 4}), indices 2 and 3 are 0.
serial8250_bytes_to_fcr() expects all four UART_FCR_R_TRIG_MAX_STATE
entries to be populated in non-decreasing order whenever entry 0 is
non-zero.  Writing 4 or more through rx_trig_bytes_store() ->
do_set_rxtrig() -> bytes_to_fcr_rxtrig() falls through the loop and
programs UART_FCR_R_TRIG_11 into UART_FCR, after which reading
rx_trig_bytes via fcr_get_rxtrig_bytes() sees rxtrig_bytes[3] == 0 and
fails with -EOPNOTSUPP.

[1] https://sashiko.dev/#/bug/linux-02824c35-118d-40cd-ba5b-57ffe1817328

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261109-8250-select-u6-64bit-v1-0-04bc8332fa34@gmail.com?part=1