openwrt/target/linux/bcm27xx/patches-4.19/950-0807-tty-amba-pl011-Avoid-rare-write-when-full-error.patch
Adrian Schmutzler 7d7aa2fd92 brcm2708: rename target to bcm27xx
This change makes the names of Broadcom targets consistent by using
the common notation based on SoC/CPU ID (which is used internally
anyway), bcmXXXX instead of brcmXXXX.
This is even used for target TITLE in make menuconfig already,
only the short target name used brcm so far.

Despite, since subtargets range from bcm2708 to bcm2711, it seems
appropriate to use bcm27xx instead of bcm2708 (again, as already done
for BOARDNAME).

This also renames the packages brcm2708-userland and brcm2708-gpu-fw.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Acked-by: Álvaro Fernández Rojas <noltari@gmail.com>
2020-02-14 14:10:51 +01:00

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1.7 KiB
Diff

From 8ef5143f743a4e922fdf0029f81452d3d7003daf Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Wed, 29 Jan 2020 09:35:19 +0000
Subject: [PATCH] tty: amba-pl011: Avoid rare write-when-full error
Under some circumstances on BCM283x processors data loss can be
observed - a single byte missing from the TX output stream. These bytes
are always the last byte of a batch of 8 written from pl011_tx_chars
when from_irq is true, meaning that the FIFO full flag is not checked
before writing.
The transmit optimisation relies on the FIFO being half-empty when the
TX interrupt is raised. Instrumenting the driver further showed that
the failure case correlated with the TX FIFO full flag being set at the
point where the last byte was written to the data register, which
explains the data loss but not how the FIFO appeared to be prematurely
full. A possible explanation is that a FIFO write was in flight at the
time the interrupt was raised, but as yet there is no hypothesis as to
how this might occur.
In the absence of a clear understanding of the failure mechanism, avoid
the problem by checking the FIFO levels before writing the last byte of
the group, which will have minimal performance impact.
Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
drivers/tty/serial/amba-pl011.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1444,6 +1444,10 @@ static bool pl011_tx_chars(struct uart_a
if (likely(from_irq) && count-- == 0)
break;
+ if (likely(from_irq) && count == 0 &&
+ pl011_read(uap, REG_FR) & UART01x_FR_TXFF)
+ break;
+
if (!pl011_tx_char(uap, xmit->buf[xmit->tail], from_irq))
break;