[PATCH v3 0/2] gpio: pcf857x: add support for reset-gpios on (most) PCA967x

[PATCH v3 0/2] gpio: pcf857x: add support for reset-gpios on (most) PCA967x

[Quentin Schulz]

The PCA9670, PCA9671, PCA9672 and PCA9673 all have a RESETN input pin
that is used to reset the I2C GPIO expander.

One needs to hold this pin low for at least 4us and the reset should be
finished after about 100us according to the datasheet[1]. Once the reset
is done, the "registers and I2C-bus state machine will be held in their
default state until the RESET input is once again HIGH.".

Because the logic is reset, the latch values eventually provided in the
Device Tree via lines-initial-states property are inapplicable so they
are simply ignored if a reset GPIO is provided.
This is eventually enforced by the Device Tree binding by making sure
both cannot be present at the same time.

Finally, the reset-gpios property is specific to PCA9670, PCA9671,
PCA9672 and PCA9673 so make it specific to those chips.

[1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 and fig 22.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
---
Changes in v3:
- wrap description of reset-gpios in dt-binding to 80 characters like
  the reset of the binding,
- add A-b and R-b trailers,
- Link to v2: https://lore.kernel.org/r/20250221-pca976x-reset-driver-v2-0-a2bcb9fdc256@cherry.de

Changes in v2:
- init n_latch to 0 again by default,
- include linux/gpio/consumer.h,
- update reset+latch comment to match what's in the datasheet from
  RESETN input chapter instead of Power-on reset chapter,
- clarify/fix expectation in commit log and binding around active level
  for the reset-gpio wrt RESET# line (ACTIVE_LOW means reset is asserted
  when the GPIO is low),
- rename rstn_gpio to reset_gpio,
- remove curly brackets around return dev_err_probe,
- use fsleep instead of usleep_range,
- use cansleep variant for setting the gpio level,
- add T-b trailers from Heiko,
- Link to v1: https://lore.kernel.org/r/20250220-pca976x-reset-driver-v1-0-6abbf043050e@cherry.de

---
Quentin Schulz (2):
      dt-bindings: gpio: nxp,pcf8575: add reset GPIO
      gpio: pcf857x: add support for reset-gpios on (most) PCA967x

 .../devicetree/bindings/gpio/nxp,pcf8575.yaml      | 37 ++++++++++++++++++++++
 drivers/gpio/gpio-pcf857x.c                        | 29 +++++++++++++++--
 2 files changed, 64 insertions(+), 2 deletions(-)
---
base-commit: d082ecbc71e9e0bf49883ee4afd435a77a5101b6
change-id: 20250219-pca976x-reset-driver-c9aa95869426

Best regards,
-- 
Quentin Schulz <quentin.schulz@cherry.de>

[PATCH v3 1/2] dt-bindings: gpio: nxp,pcf8575: add reset GPIO

[Quentin Schulz]

From: Quentin Schulz <quentin.schulz@cherry.de>

A few of the I2C GPIO expander chips supported by this binding have a
RESETN pin to be able to reset the chip. The chip is held in reset while
the pin is low, therefore the polarity of reset-gpios is expected to
reflect that, i.e. a GPIO_ACTIVE_HIGH means the GPIO will be driven high
for reset and then driven low, GPIO_ACTIVE_LOW means the GPIO will be
driven low for reset and then driven high. If a GPIO is directly routed
to RESETN pin on the IC without any inverter, GPIO_ACTIVE_LOW is thus
expected.

Out of the supported chips, only PCA9670, PCA9671, PCA9672 and PCA9673
show a RESETN pin in their datasheets. They all share the same reset
timings, that is 4+us reset pulse[0] and 100+us reset time[0].

When performing a reset, "The PCA9670 registers and I2C-bus state
machine will be held in their default state until the RESET input is
once again HIGH."[1] meaning we now know the state of each line
controlled by the GPIO expander. Therefore, setting lines-initial-states
and reset-gpios both does not make sense and their presence is XOR'ed.

[0] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf Fig 22.
[1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5

Tested-by: Heiko Stuebner <heiko@sntech.de> # exclusion logic
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
---
 .../devicetree/bindings/gpio/nxp,pcf8575.yaml      | 37 ++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml b/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml
index 3718103e966a13e1d77f73335ff73c18a3199469..8bca574bb66d491d984cb1b1665743048bcf4566 100644
--- a/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml
+++ b/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml
@@ -73,6 +73,43 @@ properties:
 
   wakeup-source: true
 
+  reset-gpios:
+    maxItems: 1
+    description:
+      GPIO controlling the (reset active LOW) RESET# pin.
+
+      The active polarity of the GPIO must translate to the low state of the
+      RESET# pin on the IC, i.e. if a GPIO is directly routed to the RESET# pin
+      without any inverter, GPIO_ACTIVE_LOW is expected.
+
+      Performing a reset makes all lines initialized to their input (pulled-up)
+      state.
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          not:
+            contains:
+              enum:
+                - nxp,pca9670
+                - nxp,pca9671
+                - nxp,pca9672
+                - nxp,pca9673
+    then:
+      properties:
+        reset-gpios: false
+
+  # lines-initial-states XOR reset-gpios
+  # Performing a reset reinitializes all lines to a known state which
+  # may not match passed lines-initial-states
+  - if:
+      required:
+        - lines-initial-states
+    then:
+      properties:
+        reset-gpios: false
+
 patternProperties:
   "^(.+-hog(-[0-9]+)?)$":
     type: object

-- 
2.48.1

[PATCH v3 2/2] gpio: pcf857x: add support for reset-gpios on (most) PCA967x

[Quentin Schulz]

From: Quentin Schulz <quentin.schulz@cherry.de>

The PCA9670, PCA9671, PCA9672 and PCA9673 all have a RESETN input pin
that is used to reset the I2C GPIO expander.

One needs to hold this pin low for at least 4us and the reset should be
finished after about 100us according to the datasheet[1]. Once the reset
is done, the "registers and I2C-bus state machine will be held in their
default state until the RESET input is once again HIGH.".

Because the logic is reset, the latch values eventually provided in the
Device Tree via lines-initial-states property are inapplicable so they
are simply ignored if a reset GPIO is provided.

[1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 and fig 22.

Tested-by: Heiko Stuebner <heiko@sntech.de> # RK3588 Tiger Haikou Video Demo
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
---
 drivers/gpio/gpio-pcf857x.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpio-pcf857x.c b/drivers/gpio/gpio-pcf857x.c
index 7c57eaeb0afeba8953d998d8eec60a65b40efb6d..2e5f5d7f886598318b753304e7e0efca54ff8b69 100644
--- a/drivers/gpio/gpio-pcf857x.c
+++ b/drivers/gpio/gpio-pcf857x.c
@@ -5,6 +5,8 @@
  * Copyright (C) 2007 David Brownell
  */
 
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/gpio/driver.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
@@ -272,12 +274,11 @@ static const struct irq_chip pcf857x_irq_chip = {
 
 static int pcf857x_probe(struct i2c_client *client)
 {
+	struct gpio_desc *reset_gpio;
 	struct pcf857x *gpio;
 	unsigned int n_latch = 0;
 	int status;
 
-	device_property_read_u32(&client->dev, "lines-initial-states", &n_latch);
-
 	/* Allocate, initialize, and register this gpio_chip. */
 	gpio = devm_kzalloc(&client->dev, sizeof(*gpio), GFP_KERNEL);
 	if (!gpio)
@@ -297,6 +298,30 @@ static int pcf857x_probe(struct i2c_client *client)
 	gpio->chip.direction_output	= pcf857x_output;
 	gpio->chip.ngpio		= (uintptr_t)i2c_get_match_data(client);
 
+	reset_gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(reset_gpio))
+		return dev_err_probe(&client->dev, PTR_ERR(reset_gpio),
+				     "failed to get reset GPIO\n");
+
+	if (reset_gpio) {
+		/* Reset already held with devm_gpiod_get_optional with GPIOD_OUT_HIGH */
+		fsleep(4); /* tw(rst) > 4us */
+		gpiod_set_value_cansleep(reset_gpio, 0);
+		fsleep(100); /* trst > 100uS */
+
+		/*
+		 * Performing a reset means "The PCA9670 registers and I2C-bus
+		 * state machine will be held in their default state until the
+		 * RESET input is once again HIGH".
+		 *
+		 * This is the same as writing 1 for all pins, which is the same
+		 * as n_latch=0, the default value of the variable.
+		 */
+	} else {
+		device_property_read_u32(&client->dev, "lines-initial-states",
+					 &n_latch);
+	}
+
 	/* NOTE:  the OnSemi jlc1562b is also largely compatible with
 	 * these parts, notably for output.  It has a low-resolution
 	 * DAC instead of pin change IRQs; and its inputs can be the

-- 
2.48.1

Re: [PATCH v3 0/2] gpio: pcf857x: add support for reset-gpios on (most) PCA967x

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>


On Mon, 24 Feb 2025 11:03:20 +0100, Quentin Schulz wrote:
> The PCA9670, PCA9671, PCA9672 and PCA9673 all have a RESETN input pin
> that is used to reset the I2C GPIO expander.
> 
> One needs to hold this pin low for at least 4us and the reset should be
> finished after about 100us according to the datasheet[1]. Once the reset
> is done, the "registers and I2C-bus state machine will be held in their
> default state until the RESET input is once again HIGH.".
> 
> [...]

Applied, thanks!

[1/2] dt-bindings: gpio: nxp,pcf8575: add reset GPIO
      commit: b28037d4f375ed36ce8abbbd31107b991792db72
[2/2] gpio: pcf857x: add support for reset-gpios on (most) PCA967x
      commit: 087f8a6b8ce93d582e0b84af538da13d735e2444

Best regards,
-- 
Bartosz Golaszewski <bartosz.golaszewski@linaro.org>