[v2] Documentation: gpio: consumer: describe active low property
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Message ID 1437199327-4410-1-git-send-email-dirk.behme@gmail.com
State New
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Dirk Behme July 18, 2015, 6:02 a.m. UTC
I've been searching for any documentation of 'the active-low property of a GPIO'
already mentioned in this documenation. But couldn't find any. Add it.

Sigend-off-by: Dirk Behme <dirk.behme@gmail.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
---
Changes in v2: Incorporate the review comments from Alexandre.

 Documentation/gpio/consumer.txt | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

Comments

Dirk Behme Aug. 15, 2015, 5:46 a.m. UTC | #1
On 18.07.2015 08:02, Dirk Behme wrote:
> I've been searching for any documentation of 'the active-low property of a GPIO'
> already mentioned in this documenation. But couldn't find any. Add it.
>
> Sigend-off-by: Dirk Behme <dirk.behme@gmail.com>
> Acked-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
> Changes in v2: Incorporate the review comments from Alexandre.
>
>   Documentation/gpio/consumer.txt | 33 +++++++++++++++++++++++++++++++++
>   1 file changed, 33 insertions(+)
>
> diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
> index 75542b9..df7c51a 100644
> --- a/Documentation/gpio/consumer.txt
> +++ b/Documentation/gpio/consumer.txt
> @@ -237,6 +237,39 @@ Note that these functions should only be used with great moderation ; a driver
>   should not have to care about the physical line level.
>
>
> +The active-low property
> +-----------------------
> +
> +As a driver should not have to care about the physical line level, all of the
> +gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
> +the *logical* value. With this they take the active-low property into account.
> +This does mean that they check whether the GPIO is configured to be active-low.
> +And if so, they manipulate the passed value before the physical line level is
> +driven.
> +
> +With this, all the gpiod_set_(array)_value_xxx() functions interpret the parameter
> +"value" as "active" ("1") or "inactive" ("0"). The physical line level will be
> +driven accordingly.
> +
> +As an example, if the active-low poperty for a dedicated GPIO is set, and the
> +gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level will be
> +driven low.
> +
> +To summarize:
> +
> +Function (example)               active-low proporty  physical line
> +gpiod_set_raw_value(desc, 0);        don't care           low
> +gpiod_set_raw_value(desc, 1);        don't care           high
> +gpiod_set_value(desc, 0);       default (active-high)     low
> +gpiod_set_value(desc, 1);       default (active-high)     high
> +gpiod_set_value(desc, 0);             active-low          high
> +gpiod_set_value(desc, 1);             active-low          low
> +
> +Please note again that the set_raw/get_raw functions should be avoided as much
> +as possible, especially by drivers which should not care about the actual physical
> +line level and worry about the logical value instead.
> +
> +
>   Set multiple GPIO outputs with a single function call
>   -----------------------------------------------------
>   The following functions set the output values of an array of GPIOs:


Any further comments on this? Could this be applied?

Dirk

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Alexandre Courbot Aug. 17, 2015, 3:01 a.m. UTC | #2
On 08/15/2015 02:46 PM, Dirk Behme wrote:
> On 18.07.2015 08:02, Dirk Behme wrote:
>> I've been searching for any documentation of 'the active-low property
>> of a GPIO'
>> already mentioned in this documenation. But couldn't find any. Add it.
>>
>> Sigend-off-by: Dirk Behme <dirk.behme@gmail.com>
>> Acked-by: Alexandre Courbot <acourbot@nvidia.com>
>> ---
>> Changes in v2: Incorporate the review comments from Alexandre.
>>
>>   Documentation/gpio/consumer.txt | 33 +++++++++++++++++++++++++++++++++
>>   1 file changed, 33 insertions(+)
>>
>> diff --git a/Documentation/gpio/consumer.txt
>> b/Documentation/gpio/consumer.txt
>> index 75542b9..df7c51a 100644
>> --- a/Documentation/gpio/consumer.txt
>> +++ b/Documentation/gpio/consumer.txt
>> @@ -237,6 +237,39 @@ Note that these functions should only be used
>> with great moderation ; a driver
>>   should not have to care about the physical line level.
>>
>>
>> +The active-low property
>> +-----------------------
>> +
>> +As a driver should not have to care about the physical line level,
>> all of the
>> +gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions
>> operate with
>> +the *logical* value. With this they take the active-low property into
>> account.
>> +This does mean that they check whether the GPIO is configured to be
>> active-low.
>> +And if so, they manipulate the passed value before the physical line
>> level is
>> +driven.
>> +
>> +With this, all the gpiod_set_(array)_value_xxx() functions interpret
>> the parameter
>> +"value" as "active" ("1") or "inactive" ("0"). The physical line
>> level will be
>> +driven accordingly.
>> +
>> +As an example, if the active-low poperty for a dedicated GPIO is set,
>> and the
>> +gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical
>> line level will be
>> +driven low.
>> +
>> +To summarize:
>> +
>> +Function (example)               active-low proporty  physical line
>> +gpiod_set_raw_value(desc, 0);        don't care           low
>> +gpiod_set_raw_value(desc, 1);        don't care           high
>> +gpiod_set_value(desc, 0);       default (active-high)     low
>> +gpiod_set_value(desc, 1);       default (active-high)     high
>> +gpiod_set_value(desc, 0);             active-low          high
>> +gpiod_set_value(desc, 1);             active-low          low
>> +
>> +Please note again that the set_raw/get_raw functions should be
>> avoided as much
>> +as possible, especially by drivers which should not care about the
>> actual physical
>> +line level and worry about the logical value instead.
>> +
>> +
>>   Set multiple GPIO outputs with a single function call
>>   -----------------------------------------------------
>>   The following functions set the output values of an array of GPIOs:
>
>
> Any further comments on this? Could this be applied?

I am ok with it - Linus?
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Michael Welling Aug. 17, 2015, 3:18 a.m. UTC | #3
On Mon, Aug 17, 2015 at 12:01:10PM +0900, Alexandre Courbot wrote:
> On 08/15/2015 02:46 PM, Dirk Behme wrote:
> >On 18.07.2015 08:02, Dirk Behme wrote:
> >>I've been searching for any documentation of 'the active-low property
> >>of a GPIO'
> >>already mentioned in this documenation. But couldn't find any. Add it.
> >>
> >>Sigend-off-by: Dirk Behme <dirk.behme@gmail.com>
> >>Acked-by: Alexandre Courbot <acourbot@nvidia.com>
> >>---
> >>Changes in v2: Incorporate the review comments from Alexandre.
> >>
> >>  Documentation/gpio/consumer.txt | 33 +++++++++++++++++++++++++++++++++
> >>  1 file changed, 33 insertions(+)
> >>
> >>diff --git a/Documentation/gpio/consumer.txt
> >>b/Documentation/gpio/consumer.txt
> >>index 75542b9..df7c51a 100644
> >>--- a/Documentation/gpio/consumer.txt
> >>+++ b/Documentation/gpio/consumer.txt
> >>@@ -237,6 +237,39 @@ Note that these functions should only be used
> >>with great moderation ; a driver
> >>  should not have to care about the physical line level.
> >>
> >>
> >>+The active-low property
> >>+-----------------------
> >>+
> >>+As a driver should not have to care about the physical line level,
> >>all of the
> >>+gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions
> >>operate with
> >>+the *logical* value. With this they take the active-low property into
> >>account.
> >>+This does mean that they check whether the GPIO is configured to be
> >>active-low.
> >>+And if so, they manipulate the passed value before the physical line
> >>level is
> >>+driven.
> >>+
> >>+With this, all the gpiod_set_(array)_value_xxx() functions interpret
> >>the parameter
> >>+"value" as "active" ("1") or "inactive" ("0"). The physical line
> >>level will be
> >>+driven accordingly.
> >>+

Property is misspelled here. poperty

> >>+As an example, if the active-low poperty for a dedicated GPIO is set,
> >>and the
> >>+gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical
> >>line level will be
> >>+driven low.
> >>+
> >>+To summarize:
> >>+

Property is also spelled wrong here too. proporty

> >>+Function (example)               active-low proporty  physical line
> >>+gpiod_set_raw_value(desc, 0);        don't care           low
> >>+gpiod_set_raw_value(desc, 1);        don't care           high
> >>+gpiod_set_value(desc, 0);       default (active-high)     low
> >>+gpiod_set_value(desc, 1);       default (active-high)     high
> >>+gpiod_set_value(desc, 0);             active-low          high
> >>+gpiod_set_value(desc, 1);             active-low          low
> >>+
> >>+Please note again that the set_raw/get_raw functions should be
> >>avoided as much
> >>+as possible, especially by drivers which should not care about the
> >>actual physical
> >>+line level and worry about the logical value instead.
> >>+
> >>+
> >>  Set multiple GPIO outputs with a single function call
> >>  -----------------------------------------------------
> >>  The following functions set the output values of an array of GPIOs:
> >
> >
> >Any further comments on this? Could this be applied?
> 
> I am ok with it - Linus?
> --
> To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
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Linus Walleij Aug. 17, 2015, 8:39 a.m. UTC | #4
On Sat, Jul 18, 2015 at 8:02 AM, Dirk Behme <dirk.behme@gmail.com> wrote:

> I've been searching for any documentation of 'the active-low property of a GPIO'
> already mentioned in this documenation. But couldn't find any. Add it.
>
> Sigend-off-by: Dirk Behme <dirk.behme@gmail.com>
> Acked-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
> Changes in v2: Incorporate the review comments from Alexandre.

I fixed some spelling and grammar and applied this patch.

Yours,
Linus Walleij
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Patch
diff mbox

diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 75542b9..df7c51a 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -237,6 +237,39 @@  Note that these functions should only be used with great moderation ; a driver
 should not have to care about the physical line level.
 
 
+The active-low property
+-----------------------
+
+As a driver should not have to care about the physical line level, all of the
+gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
+the *logical* value. With this they take the active-low property into account.
+This does mean that they check whether the GPIO is configured to be active-low.
+And if so, they manipulate the passed value before the physical line level is
+driven.
+
+With this, all the gpiod_set_(array)_value_xxx() functions interpret the parameter
+"value" as "active" ("1") or "inactive" ("0"). The physical line level will be
+driven accordingly.
+
+As an example, if the active-low poperty for a dedicated GPIO is set, and the
+gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level will be
+driven low.
+
+To summarize:
+
+Function (example)               active-low proporty  physical line
+gpiod_set_raw_value(desc, 0);        don't care           low
+gpiod_set_raw_value(desc, 1);        don't care           high
+gpiod_set_value(desc, 0);       default (active-high)     low
+gpiod_set_value(desc, 1);       default (active-high)     high
+gpiod_set_value(desc, 0);             active-low          high
+gpiod_set_value(desc, 1);             active-low          low
+
+Please note again that the set_raw/get_raw functions should be avoided as much
+as possible, especially by drivers which should not care about the actual physical
+line level and worry about the logical value instead.
+
+
 Set multiple GPIO outputs with a single function call
 -----------------------------------------------------
 The following functions set the output values of an array of GPIOs: