From eebb0f4e894f1e9577a56b337693d1051dd6ebfd Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.com>
Date: Wed, 16 Feb 2022 16:08:02 +0000
Subject: [PATCH] sc16is7xx: Fix for incorrect data being transmitted
Git-commit: eebb0f4e894f1e9577a56b337693d1051dd6ebfd
Patch-mainline: v5.17-rc6
References: git-fixes
UART drivers are meant to use the port spinlock within certain
methods, to protect against reentrancy. The sc16is7xx driver does
very little locking, presumably because when added it triggers
"scheduling while atomic" errors. This is due to the use of mutexes
within the regmap abstraction layer, and the mutex implementation's
habit of sleeping the current thread while waiting for access.
Unfortunately this lack of interlocking can lead to corruption of
outbound data, which occurs when the buffer used for I2C transmission
is used simultaneously by two threads - a work queue thread running
sc16is7xx_tx_proc, and an IRQ thread in sc16is7xx_port_irq, both
of which can call sc16is7xx_handle_tx.
An earlier patch added efr_lock, a mutex that controls access to the
EFR register. This mutex is already claimed in the IRQ handler, and
all that is required is to claim the same mutex in sc16is7xx_tx_proc.
See: https://github.com/raspberrypi/linux/issues/4885
Fixes: 6393ff1c4435 ("sc16is7xx: Use threaded IRQ")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Link: https://lore.kernel.org/r/20220216160802.1026013-1-phil@raspberrypi.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/tty/serial/sc16is7xx.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 64e7e6c8145f..38d1c0748533 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -734,12 +734,15 @@ static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
static void sc16is7xx_tx_proc(struct kthread_work *ws)
{
struct uart_port *port = &(to_sc16is7xx_one(ws, tx_work)->port);
+ struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
if ((port->rs485.flags & SER_RS485_ENABLED) &&
(port->rs485.delay_rts_before_send > 0))
msleep(port->rs485.delay_rts_before_send);
+ mutex_lock(&s->efr_lock);
sc16is7xx_handle_tx(port);
+ mutex_unlock(&s->efr_lock);
}
static void sc16is7xx_reconf_rs485(struct uart_port *port)
--
2.31.1