Re: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and output-enable

[Dong Aisheng]

On Mon, Jun 12, 2017 at 5:44 PM, jmondi <jacopo@xxxxxxxxxx> wrote:
> Hi Linus,
>
> On Sun, Jun 11, 2017 at 11:45:49PM +0200, Linus Walleij wrote:
>> On Fri, Jun 9, 2017 at 9:50 AM, jmondi <jacopo@xxxxxxxxxx> wrote:
>> > On Fri, Jun 09, 2017 at 03:26:57PM +0800, Dong Aisheng wrote:
>>
>> >> > I see three options here:
>> >> >
>> >> > 1) Add "output-buffer-enable" and "input-buffer-enable"
>> >> > we end up with
>> >> > "output-high"
>> >> > "output-low"
>> >> > "input-enable"
>> >> > "output-buffer-enable"
>> >> > "input-buffer-enable"
>> >> >
>> >> > 2) Add "output-buffer-enable" only
>> >> > we end up with
>> >> > "output-high"
>> >> > "output-low"
>> >> > "input-enable"
>> >> > "output-buffer-enable"
>> >> >
>> >> > Binding may be confusing as in one case we use "output-buffer-enable"
>> >> > while in the other "input-enable"
>> >> >
>> >> > 3) Add "output-enable" only
>> >> > "output-high"
>> >> > "output-low"
>> >> > "input-enable"
>> >> > "output-enable"
>> >> >
>> >> > As you, I don't like "output-enable" that much but it pairs better with
>> >> > "input-enable".
>> >> >
>> >> > I'll let you and DT people decide on this, as it's really an ABI definition
>> >> > problem and you have better judgment there.
>> >> >
>> >>
>> >> What's the final decision of this?
>> >
>> > I admit a was buying a bit of time and post-poned the gentle ping for
>> > any final word on this. But since you're asking I'll second your
>> > question :)
>>
>> I suspect it is time to quote
>> Documentation/process/management-style.rst
>> (Torvalds):
>>
>> 1) Decisions
>>
>> Everybody thinks managers make decisions, and that decision-making is
>> important.  The bigger and more painful the decision, the bigger the
>> manager must be to make it.  That's very deep and obvious, but it's not
>> actually true.
>>
>> The name of the game is to **avoid** having to make a decision.  In
>> particular, if somebody tells you "choose (a) or (b), we really need you
>> to decide on this", you're in trouble as a manager.  The people you
>> manage had better know the details better than you, so if they come to
>> you for a technical decision, you're screwed.  You're clearly not
>> competent to make that decision for them.
>>
>> (It goes on, it's the best part of the entire Documentation/* dir in my
>> opinion, please take the time to read it in full.)
>>
>> So: what do you guys, using this feature, and Andy, who raised serious
>> concerns, think is the right binding? That is what *I* need to know.
>
> Fair enough :)
>
> I'll try to keep this short: I don't like "output-enable", and at the
> same time I don't think "output-high" and "output-low" fit well for
> this purpose, as they electrically means something different from what
> our (and IMX) use case is: enabling/disabling input/output
> buffers internal to pin controller/gpio block HW and not driving a value
> there.
>
> This seems clear to me from the "GPIO mode pitfalls" section of
> pinctrl.txt documentation examples and from the fact that generic bindings
> did not expose an "output" flag because if you drive an output line, you
> reasonably either drive it high or low.
>
> Unfortunately I cannot convince myself that the same reasons apply
> to the input use case.  Enabling input on a pin implies the pinctrl/gpio driver
> has to enable any input buffer required to use that pin as a properly
> working input line, and enabling an input buffer implies being able to sense
> the line value from there, so I don't see that much use for "input-buffer-enable"
> alone.
>
> So, even if bindings could look a bit weird as there won't be a direct
> matching between properties names used to enable input/output buffers,
> my vote is to add "output-buffer-enable" only, and keep using the
> already there "input-enable" properties for the input use case.
>

Yes, it may be a bit weird.
I'm not pad internal details expert and can't tell much difference between
output-enable and output-buffer-enable.
I just feel a bit confuse if only using output-buffer-enable.

If enable both input and output, it becomes:
pinctrl_xxx: gpios_xxx_grp {
        pins = <
                ULP1_PAD_PTD0__PTD0
        >;
        input-enable;
        output-buffer-enable;
        bias-pull-up;
};

How about still use output-enable in pairs to input-enable but explain more
in comments?
Aslo update 'input-enable' comment to 'enable input buffer'.
e.g.
diff --git a/drivers/pinctrl/pinconf-generic.c
b/drivers/pinctrl/pinconf-generic.c
index 720a19f..96c83a4 100644
--- a/drivers/pinctrl/pinconf-generic.c
+++ b/drivers/pinctrl/pinconf-generic.c
@@ -172,6 +172,7 @@ static const struct pinconf_generic_params dt_params[] = {
        { "input-schmitt-enable", PIN_CONFIG_INPUT_SCHMITT_ENABLE, 1 },
        { "low-power-disable", PIN_CONFIG_LOW_POWER_MODE, 0 },
        { "low-power-enable", PIN_CONFIG_LOW_POWER_MODE, 1 },
+       { "output-enable", PIN_CONFIG_OUTPUT_ENABLE, 1 },
        { "output-high", PIN_CONFIG_OUTPUT, 1, },
        { "output-low", PIN_CONFIG_OUTPUT, 0, },
        { "power-source", PIN_CONFIG_POWER_SOURCE, 0 },
diff --git a/include/linux/pinctrl/pinconf-generic.h
b/include/linux/pinctrl/pinconf-generic.h
index 7620eb1..d30f4fe 100644
--- a/include/linux/pinctrl/pinconf-generic.h
+++ b/include/linux/pinctrl/pinconf-generic.h
@@ -59,9 +59,9 @@
  *     which means it will wait for signals to settle when reading inputs. The
  *     argument gives the debounce time in usecs. Setting the
  *     argument to zero turns debouncing off.
- * @PIN_CONFIG_INPUT_ENABLE: enable the pin's input.  Note that this does not
- *     affect the pin's ability to drive output.  1 enables input, 0 disables
- *     input.
+ * @PIN_CONFIG_INPUT_ENABLE: enable the pin's input buffer.  Note
that this does
+ *     not affect the pin's ability to drive output.
+ *     1 enables input, 0 disables input.
  * @PIN_CONFIG_INPUT_SCHMITT: this will configure an input pin to run in
  *     schmitt-trigger mode. If the schmitt-trigger has adjustable hysteresis,
  *     the threshold value is given on a custom format as argument when
@@ -73,6 +73,9 @@
  *     operation, if several modes of operation are supported these can be
  *     passed in the argument on a custom form, else just use argument 1
  *     to indicate low power mode, argument 0 turns low power mode off.
+ * @PIN_CONFIG_OUTPUT_ENABLE: only enable the pin's output buffer, not driving
+ *     a value.
+ *     1 enables output buffer, 0 disables output buffer.
  * @PIN_CONFIG_OUTPUT: this will configure the pin as an output. Use argument
  *     1 to indicate high level, argument 0 to indicate low level. (Please
  *     see Documentation/pinctrl.txt, section "GPIO mode pitfalls" for a

Or
invent both input-buffer-enable and output-buffer-enable and
deprecated input-enable?

Andy,
how about your comments?

Regards
Dong Aisheng

> Thanks
>    j
>
>>
>> Yours,
>> Linus Walleij