[PATCH 0/2] eeprom: at24: write-protect pin support

[PATCH 0/2] eeprom: at24: write-protect pin support

[Bartosz Golaszewski]

AT24 EEPROMs have a write-protect pin, which - when pulled high -
inhibits writes to the upper quadrant of memory (although it has been
observed that on some chips it disables writing to the entire memory
range).

On some boards, this pin is connected to a GPIO and pulled high by
default, which forces the user to manually change its state before
writing. On linux this means that we either need to hog the line all
the time, or set the GPIO value before writing from outside of the
at24 driver.

This series adds support for the write-protect pin split into two
parts. The first patch extends the relevant binding document, while
the second modifies the at24 code to pull the write-protect GPIO
low (if present) during write operations.

Bartosz Golaszewski (2):
  dt-bindings: at24: new optional property - write-protect-gpios
  eeprom: at24: add support for the write-protect pin

 Documentation/devicetree/bindings/eeprom/at24.txt |  4 ++++
 drivers/misc/eeprom/at24.c                        | 12 ++++++++++++
 2 files changed, 16 insertions(+)

-- 
2.15.1

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[PATCH 1/2] dt-bindings: at24: new optional property - write-protect-gpios

[Bartosz Golaszewski]

AT24 EEPROMs have a write-protect pin, which - when pulled high -
inhibits writes to the upper quadrant of memory (although it has been
observed that on some chips it disables writing to the entire memory
range).

On some boards, this pin is connected to a GPIO and pulled high by
default, which forces the user to manually change its state before
writing. On linux this means that we either need to hog the line all
the time, or set the GPIO value before writing from outside of the
at24 driver.

Add a new optional property to the device tree binding document, which
allows to specify the GPIO line to which the write-protect pin is
connected.

Signed-off-by: Bartosz Golaszewski <brgl-ARrdPY/1zhM@public.gmane.org>
---
 Documentation/devicetree/bindings/eeprom/at24.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/eeprom/at24.txt b/Documentation/devicetree/bindings/eeprom/at24.txt
index a0415b8471bb..e489654c02ae 100644
--- a/Documentation/devicetree/bindings/eeprom/at24.txt
+++ b/Documentation/devicetree/bindings/eeprom/at24.txt
@@ -43,10 +43,14 @@ Optional properties:
 			eeprom does not automatically roll over reads to the next
 			slave address. Please consult the manual of your device.
 
+  - write-protect-gpios: GPIO to which the write-protect pin of the chip is
+                         is connected.
+
 Example:
 
 eeprom@52 {
 	compatible = "atmel,24c32";
 	reg = <0x52>;
 	pagesize = <32>;
+	write-protect-gpios = <&gpio1 3 0>;
 };
-- 
2.15.1

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Re: [PATCH 1/2] dt-bindings: at24: new optional property - write-protect-gpios

[Andy Shevchenko]

On Tue, Dec 19, 2017 at 6:14 PM, Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> AT24 EEPROMs have a write-protect pin, which - when pulled high -
> inhibits writes to the upper quadrant of memory (although it has been
> observed that on some chips it disables writing to the entire memory
> range).
>
> On some boards, this pin is connected to a GPIO and pulled high by
> default, which forces the user to manually change its state before
> writing. On linux this means that we either need to hog the line all
> the time, or set the GPIO value before writing from outside of the
> at24 driver.
>
> Add a new optional property to the device tree binding document, which
> allows to specify the GPIO line to which the write-protect pin is
> connected.
>

> +  - write-protect-gpios: GPIO to which the write-protect pin of the chip is

The rule of thumb is to check what is de facto state of the properties
like this, i.e.

% git grep -n wp-gpio -- Documentation/ | wc -l
14
% git grep -n write-protect-gpio -- Documentation/ | wc -l
0

I think it means something.

-- 
With Best Regards,
Andy Shevchenko

[PATCH 2/2] eeprom: at24: add support for the write-protect pin

[Bartosz Golaszewski]

AT24 EEPROMs have a write-protect pin, which - when pulled high -
inhibits writes to the upper quadrant of memory (although it has been
observed that on some chips it disables writing to the entire memory
range).

On some boards, this pin is connected to a GPIO and pulled high by
default, which forces the user to manually change its state before
writing. On linux this means that we either need to hog the line all
the time, or set the GPIO value before writing from outside of the
at24 driver.

Make the driver check if the write-protect GPIO was defined in the
device tree and pull it low whenever writing to the EEPROM.

Signed-off-by: Bartosz Golaszewski <brgl-ARrdPY/1zhM@public.gmane.org>
---
 drivers/misc/eeprom/at24.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index b44a3d2b2b20..8cb0883dd297 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -27,6 +27,7 @@
 #include <linux/regmap.h>
 #include <linux/platform_data/at24.h>
 #include <linux/pm_runtime.h>
+#include <linux/gpio/consumer.h>
 
 /*
  * I2C EEPROMs from most vendors are inexpensive and mostly interchangeable.
@@ -77,6 +78,8 @@ struct at24_data {
 	struct nvmem_config nvmem_config;
 	struct nvmem_device *nvmem;
 
+	struct gpio_desc *wp_gpio;
+
 	/*
 	 * Some chips tie up multiple I2C addresses; dummy devices reserve
 	 * them for us, and we'll use them with SMBus calls.
@@ -442,12 +445,14 @@ static int at24_write(void *priv, unsigned int off, void *val, size_t count)
 	 * from this host, but not from other I2C masters.
 	 */
 	mutex_lock(&at24->lock);
+	gpiod_set_value_cansleep(at24->wp_gpio, 0);
 
 	while (count) {
 		int status;
 
 		status = at24_regmap_write(at24, buf, off, count);
 		if (status < 0) {
+			gpiod_set_value_cansleep(at24->wp_gpio, 1);
 			mutex_unlock(&at24->lock);
 			pm_runtime_put(dev);
 			return status;
@@ -457,6 +462,7 @@ static int at24_write(void *priv, unsigned int off, void *val, size_t count)
 		count -= status;
 	}
 
+	gpiod_set_value_cansleep(at24->wp_gpio, 1);
 	mutex_unlock(&at24->lock);
 
 	pm_runtime_put(dev);
@@ -604,6 +610,12 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 	at24->num_addresses = num_addresses;
 	at24->offset_adj = at24_get_offset_adj(chip.flags, chip.byte_len);
 
+	at24->wp_gpio = devm_gpiod_get_optional(&client->dev,
+						"write-protect",
+						GPIOD_OUT_HIGH);
+	if (IS_ERR(at24->wp_gpio))
+		return PTR_ERR(at24->wp_gpio);
+
 	at24->client[0].client = client;
 	at24->client[0].regmap = devm_regmap_init_i2c(client, &regmap_config);
 	if (IS_ERR(at24->client[0].regmap))
-- 
2.15.1

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Re: [PATCH 0/2] eeprom: at24: write-protect pin support

[Bartosz Golaszewski]

2017-12-19 17:14 GMT+01:00 Bartosz Golaszewski <brgl-ARrdPY/1zhM@public.gmane.org>:
> AT24 EEPROMs have a write-protect pin, which - when pulled high -
> inhibits writes to the upper quadrant of memory (although it has been
> observed that on some chips it disables writing to the entire memory
> range).
>
> On some boards, this pin is connected to a GPIO and pulled high by
> default, which forces the user to manually change its state before
> writing. On linux this means that we either need to hog the line all
> the time, or set the GPIO value before writing from outside of the
> at24 driver.
>
> This series adds support for the write-protect pin split into two
> parts. The first patch extends the relevant binding document, while
> the second modifies the at24 code to pull the write-protect GPIO
> low (if present) during write operations.
>
> Bartosz Golaszewski (2):
>   dt-bindings: at24: new optional property - write-protect-gpios
>   eeprom: at24: add support for the write-protect pin
>
>  Documentation/devicetree/bindings/eeprom/at24.txt |  4 ++++
>  drivers/misc/eeprom/at24.c                        | 12 ++++++++++++
>  2 files changed, 16 insertions(+)
>
> --
> 2.15.1
>

Superseded by v2.

Thanks,
Bartosz
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