From: "Maciej W. Rozycki" <macro@orcam.me.uk>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>
Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/2] serial: 8250: Define RX trigger levels for OxSemi 950 devices
Date: Sat, 26 Jun 2021 06:11:51 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.2106260608480.37803@angie.orcam.me.uk> (raw)
In-Reply-To: <alpine.DEB.2.21.2106260539240.37803@angie.orcam.me.uk>
Oxford Semiconductor 950 serial port devices have a 128-byte FIFO and in
the enhanced (650) mode, which we select in `autoconfig_has_efr' with
the ECB bit set in the EFR register, they support the receive interrupt
trigger level selectable with FCR bits 7:6 from the set of 16, 32, 112,
120. This applies to the original OX16C950 discrete UART[1] as well as
950 cores embedded into more complex devices.
For these devices we set the default to 112, which sets an excessively
high level of 112 or 7/8 of the FIFO capacity, unlike with other port
types where we choose at most 1/2 of their respective FIFO capacities.
Additionally we don't make the trigger level configurable. Consequently
frequent input overruns happen with high bit rates where hardware flow
control cannot be used (e.g. terminal applications) even with otherwise
highly-performant systems.
Lower the default receive interrupt trigger level to 32 then, and make
it configurable. Document the trigger levels along with other port
types, including the set of 16, 32, 64, 112 for the transmit interrupt
as well[2].
References:
[1] "OX16C950 rev B High Performance UART with 128 byte FIFOs", Oxford
Semiconductor, Inc., DS-0031, Sep 05, Table 10: "Receiver Trigger
Levels", p. 22
[2] same, Table 9: "Transmit Interrupt Trigger Levels", p. 22
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
---
No change from v1.
---
drivers/tty/serial/8250/8250_port.c | 3 ++-
include/uapi/linux/serial_reg.h | 1 +
2 files changed, 3 insertions(+), 1 deletion(-)
linux-serial-8250-oxsemi-fifo.diff
Index: linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c
===================================================================
--- linux-malta-cbus-uart.orig/drivers/tty/serial/8250/8250_port.c
+++ linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c
@@ -122,7 +122,8 @@ static const struct serial8250_config ua
.name = "16C950/954",
.fifo_size = 128,
.tx_loadsz = 128,
- .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10,
+ .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01,
+ .rxtrig_bytes = {16, 32, 112, 120},
/* UART_CAP_EFR breaks billionon CF bluetooth card. */
.flags = UART_CAP_FIFO | UART_CAP_SLEEP,
},
Index: linux-malta-cbus-uart/include/uapi/linux/serial_reg.h
===================================================================
--- linux-malta-cbus-uart.orig/include/uapi/linux/serial_reg.h
+++ linux-malta-cbus-uart/include/uapi/linux/serial_reg.h
@@ -62,6 +62,7 @@
* ST16C654: 8 16 56 60 8 16 32 56 PORT_16654
* TI16C750: 1 16 32 56 xx xx xx xx PORT_16750
* TI16C752: 8 16 56 60 8 16 32 56
+ * OX16C950: 16 32 112 120 16 32 64 112 PORT_16C950
* Tegra: 1 4 8 14 16 8 4 1 PORT_TEGRA
*/
#define UART_FCR_R_TRIG_00 0x00
prev parent reply other threads:[~2021-06-26 4:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-26 4:11 [PATCH v2 0/2] serial: 8250: Fixes for Oxford Semiconductor 950 UARTs Maciej W. Rozycki
2021-06-26 4:11 ` [PATCH v2 1/2] serial: 8250: Add proper clock handling for OxSemi PCIe devices Maciej W. Rozycki
2021-07-12 20:15 ` andy
2021-07-13 1:52 ` Maciej W. Rozycki
2021-07-13 7:19 ` Andy Shevchenko
2021-07-15 19:49 ` Maciej W. Rozycki
2021-07-19 14:55 ` Andy Shevchenko
2022-02-12 8:41 ` Maciej W. Rozycki
2022-03-18 13:40 ` Andy Shevchenko
2022-03-23 21:59 ` Maciej W. Rozycki
2022-03-24 11:28 ` Andy Shevchenko
2021-06-26 4:11 ` Maciej W. Rozycki [this message]
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