File serial-8250-Define-RX-trigger-levels-for-OxSemi... of Package linux-glibc-devel

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File serial-8250-Define-RX-trigger-levels-for-OxSemi-950-.patch of Package linux-glibc-devel

From 84f8b1a65627337720675a7c82064fa05ff5afc9 Mon Sep 17 00:00:00 2001
From: "Maciej W. Rozycki" <macro@orcam.me.uk>
Date: Sat, 26 Jun 2021 06:11:51 +0200
Subject: [PATCH] serial: 8250: Define RX trigger levels for OxSemi 950 devices
Git-commit: d7aff291d069c4418285f3c8ee27b0ff67ce5998
Patch-mainline: v5.15-rc1
References: stable-5.14.6

[ Upstream commit d7aff291d069c4418285f3c8ee27b0ff67ce5998 ]

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>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2106260608480.37803@angie.orcam.me.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/tty/serial/8250/8250_port.c | 3 ++-
 include/uapi/linux/serial_reg.h     | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/serial_reg.h b/include/uapi/linux/serial_reg.h
index be07b5470f4b..f51bc8f36813 100644
--- a/include/linux/serial_reg.h
+++ b/include/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
-- 
2.26.2

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File serial-8250-Define-RX-trigger-levels-for-OxSemi-950-.patch of Package linux-glibc-devel

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