[PATCH v2 0/2] eeprom: at24: write-protect pin support

[PATCH v2 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.

v1 -> v2:
- renamed the DT property to wp-gpios

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

 Documentation/devicetree/bindings/eeprom/at24.txt |  3 +++
 drivers/misc/eeprom/at24.c                        | 11 +++++++++++
 2 files changed, 14 insertions(+)

-- 
2.15.1

[PATCH v2 1/2] dt-bindings: at24: new optional property - wp-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@bgdev.pl>
---
 Documentation/devicetree/bindings/eeprom/at24.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/devicetree/bindings/eeprom/at24.txt b/Documentation/devicetree/bindings/eeprom/at24.txt
index a0415b8471bb..cbc80e194ac6 100644
--- a/Documentation/devicetree/bindings/eeprom/at24.txt
+++ b/Documentation/devicetree/bindings/eeprom/at24.txt
@@ -43,10 +43,13 @@ Optional properties:
 			eeprom does not automatically roll over reads to the next
 			slave address. Please consult the manual of your device.
 
+  - wp-gpios: GPIO to which the write-protect pin of the chip is connected.
+
 Example:
 
 eeprom@52 {
 	compatible = "atmel,24c32";
 	reg = <0x52>;
 	pagesize = <32>;
+	wp-gpios = <&gpio1 3 0>;
 };
-- 
2.15.1

Re: [PATCH v2 1/2] dt-bindings: at24: new optional property - wp-gpios

[Rob Herring]

On Wed, Dec 20, 2017 at 09:26:32AM +0100, Bartosz Golaszewski 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.
> 
> Signed-off-by: Bartosz Golaszewski <brgl-ARrdPY/1zhM@public.gmane.org>
> ---
>  Documentation/devicetree/bindings/eeprom/at24.txt | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
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[PATCH v2 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@bgdev.pl>
---
 drivers/misc/eeprom/at24.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index b44a3d2b2b20..4456e192681c 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 +610,11 @@ 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,
+						"wp", 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

Re: [PATCH v2 0/2] eeprom: at24: write-protect pin support

[Andy Shevchenko]

On Wed, Dec 20, 2017 at 10:26 AM, Bartosz Golaszewski <brgl-ARrdPY/1zhM@public.gmane.org> 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.
>
> 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.
>

Reviewed-by: Andy Shevchenko <andy.shevchenko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

A one totally minor nit: if it possible now to have one line where
devm_gpiod_get_optional() is called?
You may ignore this nit anyway.

> v1 -> v2:
> - renamed the DT property to wp-gpios
>
> Bartosz Golaszewski (2):
>   dt-bindings: at24: new optional property - wp-gpios
>   eeprom: at24: add support for the write-protect pin
>
>  Documentation/devicetree/bindings/eeprom/at24.txt |  3 +++
>  drivers/misc/eeprom/at24.c                        | 11 +++++++++++
>  2 files changed, 14 insertions(+)
>
> --
> 2.15.1
>



-- 
With Best Regards,
Andy Shevchenko
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Re: [PATCH v2 0/2] eeprom: at24: write-protect pin support

[Bartosz Golaszewski]

2017-12-20 11:21 GMT+01:00 Andy Shevchenko <andy.shevchenko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
> On Wed, Dec 20, 2017 at 10:26 AM, Bartosz Golaszewski <brgl-ARrdPY/1zhM@public.gmane.org> 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.
>>
>> 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.
>>
>
> Reviewed-by: Andy Shevchenko <andy.shevchenko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> A one totally minor nit: if it possible now to have one line where
> devm_gpiod_get_optional() is called?
> You may ignore this nit anyway.
>

Hi Andy,

I'm afraid I don't understand what you mean here. I do use
devm_gpiod_get_optional() in patch 2/2.

Thanks,
Bartosz
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Re: [PATCH v2 0/2] eeprom: at24: write-protect pin support

[Andy Shevchenko]

On Wed, Dec 20, 2017 at 2:41 PM, Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> 2017-12-20 11:21 GMT+01:00 Andy Shevchenko <andy.shevchenko@gmail.com>:
>> On Wed, Dec 20, 2017 at 10:26 AM, 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.
>>>
>>> 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.
>>>
>>
>> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
>>
>> A one totally minor nit: if it possible now to have one line where
>> devm_gpiod_get_optional() is called?
>> You may ignore this nit anyway.
>>
>
> Hi Andy,
>
> I'm afraid I don't understand what you mean here. I do use
> devm_gpiod_get_optional() in patch 2/2.

I meant to do something like
...->wp_gpio = devm_gpiod_get_optional(...);
if (IS_ERR(...))
  return ...;

So, note that the first is occupied only one line.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 0/2] eeprom: at24: write-protect pin support

[Bartosz Golaszewski]

2017-12-20 16:00 GMT+01:00 Andy Shevchenko <andy.shevchenko@gmail.com>:
> On Wed, Dec 20, 2017 at 2:41 PM, Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>> 2017-12-20 11:21 GMT+01:00 Andy Shevchenko <andy.shevchenko@gmail.com>:
>>> On Wed, Dec 20, 2017 at 10:26 AM, 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.
>>>>
>>>> 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.
>>>>
>>>
>>> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
>>>
>>> A one totally minor nit: if it possible now to have one line where
>>> devm_gpiod_get_optional() is called?
>>> You may ignore this nit anyway.
>>>
>>
>> Hi Andy,
>>
>> I'm afraid I don't understand what you mean here. I do use
>> devm_gpiod_get_optional() in patch 2/2.
>
> I meant to do something like
> ...->wp_gpio = devm_gpiod_get_optional(...);
> if (IS_ERR(...))
>   return ...;
>
> So, note that the first is occupied only one line.
>
> --
> With Best Regards,
> Andy Shevchenko

Oh, now I get it.

It doesn't fit into 80 characters if we use &client->dev as the first
argument, but I see that client->dev is used extensively in probe() so
we could probably use a separate struct device *dev helper variable
for that. I'll note it for future refactoring that will happen soon. I
prefer that this patch stays as it is though.

Thanks,
Bartosz