i2c-mux-pca954x: Force reset on probe if available

Message ID 1525174932-8865-1-git-send-email-mike.looijmans@topic.nl
State New
Delegated to: Peter Rosin
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  • i2c-mux-pca954x: Force reset on probe if available
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Commit Message

Mike Looijmans May 1, 2018, 11:42 a.m.
Instead of just hogging the reset GPIO into deactivated state, activate and
then de-activate the reset. This allows for better recovery if the CPU was
reset halfway through an I2C transaction for example.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
---
 drivers/i2c/muxes/i2c-mux-pca954x.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Peter Rosin May 8, 2018, 6:36 a.m. | #1
On 2018-05-01 13:42, Mike Looijmans wrote:
> Instead of just hogging the reset GPIO into deactivated state, activate and
> then de-activate the reset. This allows for better recovery if the CPU was
> reset halfway through an I2C transaction for example.

I can't see any problems with this, and a reset at load time can certainly
be a benefit. Some questions below though...

Cheers,
Peter

> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
> ---
>  drivers/i2c/muxes/i2c-mux-pca954x.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 09bafd3..13e10d0 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -36,6 +36,7 @@
>   */
>  
>  #include <linux/device.h>
> +#include <linux/delay.h>
>  #include <linux/gpio/consumer.h>
>  #include <linux/i2c.h>
>  #include <linux/i2c-mux.h>
> @@ -389,10 +390,17 @@ static int pca954x_probe(struct i2c_client *client,
>  	i2c_set_clientdata(client, muxc);
>  	data->client = client;
>  
> -	/* Get the mux out of reset if a reset GPIO is specified. */
> -	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_LOW);
> +	/* Reset the mux if a reset GPIO is specified. */
> +	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
>  	if (IS_ERR(gpio))
>  		return PTR_ERR(gpio);
> +	if (gpio) {
> +		/* Datasheet specifies a 4 ns reset-low time */
> +		udelay(1);

ndelay(4) ?

> +		gpiod_set_value_cansleep(gpio, 0);
> +		/* Datasheet specifies a 500 ns reset recovery time */
> +		udelay(1);

ndelay(500) ?

> +	}
>  
>  	match = of_match_device(of_match_ptr(pca954x_of_match), &client->dev);
>  	if (match)
>
Mike Looijmans May 8, 2018, 8:06 a.m. | #2
´╗┐On 08-05-18 08:36, Peter Rosin wrote:
> On 2018-05-01 13:42, Mike Looijmans wrote:
>> Instead of just hogging the reset GPIO into deactivated state, activate and
>> then de-activate the reset. This allows for better recovery if the CPU was
>> reset halfway through an I2C transaction for example.
> 
> I can't see any problems with this, and a reset at load time can certainly
> be a benefit. Some questions below though...
> 
> Cheers,
> Peter
> 
>> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
>> ---
>>   drivers/i2c/muxes/i2c-mux-pca954x.c | 12 ++++++++++--
>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
>> index 09bafd3..13e10d0 100644
>> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
>> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
>> @@ -36,6 +36,7 @@
>>    */
>>   
>>   #include <linux/device.h>
>> +#include <linux/delay.h>
>>   #include <linux/gpio/consumer.h>
>>   #include <linux/i2c.h>
>>   #include <linux/i2c-mux.h>
>> @@ -389,10 +390,17 @@ static int pca954x_probe(struct i2c_client *client,
>>   	i2c_set_clientdata(client, muxc);
>>   	data->client = client;
>>   
>> -	/* Get the mux out of reset if a reset GPIO is specified. */
>> -	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_LOW);
>> +	/* Reset the mux if a reset GPIO is specified. */
>> +	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
>>   	if (IS_ERR(gpio))
>>   		return PTR_ERR(gpio);
>> +	if (gpio) {
>> +		/* Datasheet specifies a 4 ns reset-low time */
>> +		udelay(1);
> 
> ndelay(4) ?
> 

I have several reasons for making it much much longer:
- A true 4ns pulse might not make it through the GPIO controller (on some 
chips, the GPIO controller runs at 1/10th of the CPU speed or even less)
- Board designers tend to treat RESET signals as "DC", so a 250MHz pulse might 
not make it through. There may be level converters and open-drain drives in 
the signal path as well.
- I've only looked it op on a few chips, others may have different values

I think best is to just remove the comment line, it doesn't really help.

>> +		gpiod_set_value_cansleep(gpio, 0);
>> +		/* Datasheet specifies a 500 ns reset recovery time */
>> +		udelay(1);
> 
> ndelay(500) ?

Similar reasons as above.

> 
>> +	}
>>   
>>   	match = of_match_device(of_match_ptr(pca954x_of_match), &client->dev);
>>   	if (match)
>>
> 



Kind regards,

Mike Looijmans
System Expert

TOPIC Products
Materiaalweg 4, NL-5681 RJ Best
Postbus 440, NL-5680 AK Best
Telefoon: +31 (0) 499 33 69 79
E-mail: mike.looijmans@topicproducts.com
Website: www.topicproducts.com

Please consider the environment before printing this e-mail
Peter Rosin May 19, 2018, 9:58 p.m. | #3
On 2018-05-08 10:06, Mike Looijmans wrote:
> On 08-05-18 08:36, Peter Rosin wrote:
>> On 2018-05-01 13:42, Mike Looijmans wrote:
>>> Instead of just hogging the reset GPIO into deactivated state, activate and
>>> then de-activate the reset. This allows for better recovery if the CPU was
>>> reset halfway through an I2C transaction for example.
>>
>> I can't see any problems with this, and a reset at load time can certainly
>> be a benefit. Some questions below though...
>>
>> Cheers,
>> Peter
>>
>>> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
>>> ---
>>>   drivers/i2c/muxes/i2c-mux-pca954x.c | 12 ++++++++++--
>>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
>>> index 09bafd3..13e10d0 100644
>>> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
>>> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
>>> @@ -36,6 +36,7 @@
>>>    */
>>>   
>>>   #include <linux/device.h>
>>> +#include <linux/delay.h>
>>>   #include <linux/gpio/consumer.h>
>>>   #include <linux/i2c.h>
>>>   #include <linux/i2c-mux.h>
>>> @@ -389,10 +390,17 @@ static int pca954x_probe(struct i2c_client *client,
>>>   	i2c_set_clientdata(client, muxc);
>>>   	data->client = client;
>>>   
>>> -	/* Get the mux out of reset if a reset GPIO is specified. */
>>> -	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_LOW);
>>> +	/* Reset the mux if a reset GPIO is specified. */
>>> +	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
>>>   	if (IS_ERR(gpio))
>>>   		return PTR_ERR(gpio);
>>> +	if (gpio) {
>>> +		/* Datasheet specifies a 4 ns reset-low time */
>>> +		udelay(1);
>>
>> ndelay(4) ?
>>
> 
> I have several reasons for making it much much longer:
> - A true 4ns pulse might not make it through the GPIO controller (on some 
> chips, the GPIO controller runs at 1/10th of the CPU speed or even less)
> - Board designers tend to treat RESET signals as "DC", so a 250MHz pulse might 
> not make it through. There may be level converters and open-drain drives in 
> the signal path as well.
> - I've only looked it op on a few chips, others may have different values
> 
> I think best is to just remove the comment line, it doesn't really help.
> 
>>> +		gpiod_set_value_cansleep(gpio, 0);
>>> +		/* Datasheet specifies a 500 ns reset recovery time */
>>> +		udelay(1);
>>
>> ndelay(500) ?
> 
> Similar reasons as above.

Agreed, sounds sane.

Applied to i2c-mux/for-next with minor tweaks to the subject and comments.

Cheers,
Peter

>>
>>> +	}
>>>   
>>>   	match = of_match_device(of_match_ptr(pca954x_of_match), &client->dev);
>>>   	if (match)
>>>
>>
> 
> 
> 
> Kind regards,
> 
> Mike Looijmans
> System Expert
> 
> TOPIC Products
> Materiaalweg 4, NL-5681 RJ Best
> Postbus 440, NL-5680 AK Best
> Telefoon: +31 (0) 499 33 69 79
> E-mail: mike.looijmans@topicproducts.com
> Website: www.topicproducts.com
> 
> Please consider the environment before printing this e-mail
> 
> 
>

Patch

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 09bafd3..13e10d0 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -36,6 +36,7 @@ 
  */
 
 #include <linux/device.h>
+#include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/i2c-mux.h>
@@ -389,10 +390,17 @@  static int pca954x_probe(struct i2c_client *client,
 	i2c_set_clientdata(client, muxc);
 	data->client = client;
 
-	/* Get the mux out of reset if a reset GPIO is specified. */
-	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_LOW);
+	/* Reset the mux if a reset GPIO is specified. */
+	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
 	if (IS_ERR(gpio))
 		return PTR_ERR(gpio);
+	if (gpio) {
+		/* Datasheet specifies a 4 ns reset-low time */
+		udelay(1);
+		gpiod_set_value_cansleep(gpio, 0);
+		/* Datasheet specifies a 500 ns reset recovery time */
+		udelay(1);
+	}
 
 	match = of_match_device(of_match_ptr(pca954x_of_match), &client->dev);
 	if (match)