This is a note to let you know that I've just added the patch titled
serial: sc16is7xx: fix bug when first setting GPIO direction
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-sc16is7xx-fix-bug-when-first-setting-gpio-direction.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 9baeea723c0fb9c3ba9a336369f758ed9bc6831d Mon Sep 17 00:00:00 2001
From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
Date: Mon, 7 Aug 2023 17:45:55 -0400
Subject: serial: sc16is7xx: fix bug when first setting GPIO direction
From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
commit 9baeea723c0fb9c3ba9a336369f758ed9bc6831d upstream.
When configuring a pin as an output pin with a value of logic 0, we
end up as having a value of logic 1 on the output pin. Setting a
logic 0 a second time (or more) after that will correctly output a
logic 0 on the output pin.
By default, all GPIO pins are configured as inputs. When we enter
sc16is7xx_gpio_direction_output() for the first time, we first set the
desired value in IOSTATE, and then we configure the pin as an output.
The datasheet states that writing to IOSTATE register will trigger a
transfer of the value to the I/O pin configured as output, so if the
pin is configured as an input, nothing will be transferred.
Therefore, set the direction first in IODIR, and then set the desired
value in IOSTATE.
This is what is done in NXP application note AN10587.
Fixes: dfeae619d781 ("serial: sc16is7xx")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
Reviewed-by: Lech Perczak <lech.perczak@xxxxxxxxxxxxxxx>
Tested-by: Lech Perczak <lech.perczak@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230807214556.540627-6-hugo@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/sc16is7xx.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -1166,9 +1166,18 @@ static int sc16is7xx_gpio_direction_outp
state |= BIT(offset);
else
state &= ~BIT(offset);
- sc16is7xx_port_write(port, SC16IS7XX_IOSTATE_REG, state);
+
+ /*
+ * If we write IOSTATE first, and then IODIR, the output value is not
+ * transferred to the corresponding I/O pin.
+ * The datasheet states that each register bit will be transferred to
+ * the corresponding I/O pin programmed as output when writing to
+ * IOSTATE. Therefore, configure direction first with IODIR, and then
+ * set value after with IOSTATE.
+ */
sc16is7xx_port_update(port, SC16IS7XX_IODIR_REG, BIT(offset),
BIT(offset));
+ sc16is7xx_port_write(port, SC16IS7XX_IOSTATE_REG, state);
return 0;
}
Patches currently in stable-queue which might be from hvilleneuve@xxxxxxxxxxxx are
queue-5.4/serial-sc16is7xx-fix-bug-when-first-setting-gpio-direction.patch
