Patch "gpio: ts4900: Do not set DAT and OE together" has been added to the 4.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    gpio: ts4900: Do not set DAT and OE together

to the 4.9-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:
     gpio-ts4900-do-not-set-dat-and-oe-together.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 812210301fe1239ec57a362d9d90e6f9d3041454
Author: Mark Featherston <mark@xxxxxxxxxxxxxx>
Date:   Wed Mar 9 17:16:16 2022 -0800

    gpio: ts4900: Do not set DAT and OE together
    
    [ Upstream commit 03fe003547975680fdb9ff5ab0e41cb68276c4f2 ]
    
    This works around an issue with the hardware where both OE and
    DAT are exposed in the same register. If both are updated
    simultaneously, the harware makes no guarantees that OE or DAT
    will actually change in any given order and may result in a
    glitch of a few ns on a GPIO pin when changing direction and value
    in a single write.
    
    Setting direction to input now only affects OE bit. Setting
    direction to output updates DAT first, then OE.
    
    Fixes: 9c6686322d74 ("gpio: add Technologic I2C-FPGA gpio support")
    Signed-off-by: Mark Featherston <mark@xxxxxxxxxxxxxx>
    Signed-off-by: Kris Bahnsen <kris@xxxxxxxxxxxxxx>
    Signed-off-by: Bartosz Golaszewski <brgl@xxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpio/gpio-ts4900.c b/drivers/gpio/gpio-ts4900.c
index 5bd21725e604..930a6098b758 100644
--- a/drivers/gpio/gpio-ts4900.c
+++ b/drivers/gpio/gpio-ts4900.c
@@ -1,7 +1,7 @@
 /*
  * Digital I/O driver for Technologic Systems I2C FPGA Core
  *
- * Copyright (C) 2015 Technologic Systems
+ * Copyright (C) 2015, 2018 Technologic Systems
  * Copyright (C) 2016 Savoir-Faire Linux
  *
  * This program is free software; you can redistribute it and/or
@@ -52,19 +52,33 @@ static int ts4900_gpio_direction_input(struct gpio_chip *chip,
 {
 	struct ts4900_gpio_priv *priv = gpiochip_get_data(chip);
 
-	/*
-	 * This will clear the output enable bit, the other bits are
-	 * dontcare when this is cleared
+	/* Only clear the OE bit here, requires a RMW. Prevents potential issue
+	 * with OE and data getting to the physical pin at different times.
 	 */
-	return regmap_write(priv->regmap, offset, 0);
+	return regmap_update_bits(priv->regmap, offset, TS4900_GPIO_OE, 0);
 }
 
 static int ts4900_gpio_direction_output(struct gpio_chip *chip,
 					unsigned int offset, int value)
 {
 	struct ts4900_gpio_priv *priv = gpiochip_get_data(chip);
+	unsigned int reg;
 	int ret;
 
+	/* If changing from an input to an output, we need to first set the
+	 * proper data bit to what is requested and then set OE bit. This
+	 * prevents a glitch that can occur on the IO line
+	 */
+	regmap_read(priv->regmap, offset, &reg);
+	if (!(reg & TS4900_GPIO_OE)) {
+		if (value)
+			reg = TS4900_GPIO_OUT;
+		else
+			reg &= ~TS4900_GPIO_OUT;
+
+		regmap_write(priv->regmap, offset, reg);
+	}
+
 	if (value)
 		ret = regmap_write(priv->regmap, offset, TS4900_GPIO_OE |
 							 TS4900_GPIO_OUT);