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

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  Re: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and output-enable Dong Aisheng <dongas86@gmail.com> - 2017-05-23 12:10 +0200
    Re: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and  output-enable jmondi <jacopo@jmondi.org> - 2017-05-23 20:40 +0200

#1647911 — Re: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and output-enable

On Tue, May 9, 2017 at 5:19 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Mon, May 8, 2017 at 7:25 PM, jmondi <jacopo@jmondi.org> wrote:
>
>> From my perspective these flags are configurations internal to the pin
>> controller hardware used to enable/disable input buffers when a pin needs to
>> perform in both direction.
>> The level of detail I can provide on this is the logical diagram we have pointed
>> you to already.
>>
>> As I assume you are trying to get this answer from us in order to
>> avoid duplicating things in pin controller sub-system, and I
>> understand this, but my question here was "can we have those flags as part
>> of the pinmux property argument list, as that property description
>> seems to allow us to do that, instead of making them generic pin
>> configuration properties and upset other developers?"
>
> Pinmux with all it's magic flags baked into one is not any better
> or any more readable. The solution is already very pretty except
> for these two flags which I am sure we can agree on a way forward
> for.
>
> What we choose between is not this or another less transparent
> pin configuration mechanism, the mechanism (whether magic bits
> to pinmux or reasonable properties) does not matter.
>
> There is a strong preference to use the generic bindings.
>
> So the discussion is whether to use:
>
> bi-directional;
> output-enable;
>
> Or some already defined config flags.
>
> If these are too idiomatic to be used by others, they should anyways
> look similar, like:
>
> renesas,bi-directional;
> renesas,output-enable;
>
> Like the Qualcomm weirdness found in drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
>
> qcom,pull-up-strength = <..>;
>
> Check how they use
> #define PMIC_GPIO_CONF_PULL_UP                 (PIN_CONFIG_END + 1)
>
> Etc.
>
>> Anyway, I still fail to see why those configuration flags, only
>> affecting the way the pin controller hardware enables/disables
>> its internal buffers and its internal operations have to be
>> described in term of their externally visible electrically characteristics.
>
> To me internal vs external is not what matters. What matters is
> if this is likely to pop up in more platforms, and then the property
> should be generic.
>
> The generic pin config definitions are likely to be picked up by other
> standards and even be inspiration to hardware engineers so that
> is why it matters so much.
>
>> To me, what already exists are pin configuration properties generic to
>> the whole pin controller subsystem, and I understand you don't want to
>> see duplication there.
>>
>> At the same time, to me, those flags are settings the pin controller
>> wants to have specified by software to overcome its hw design flaws,
>> and are intended to configure its internal buffers in a way it cannot
>> do by itself for some very specific operation modes (they are listed
>> in the hw reference manual, it's not something you can chose to
>> configure or not, if you want a pin working in i2c mode, you HAVE to
>> pass those flags to pin controller).
>
> Sounds like a case for
>
> renesas,bi-directional;
> renesas,output-enable;
>
> following the Qualcomm pattern in that case.
>
> But let's see if something else comes out of this discussion.
>

I did not follow too much.
But it seems IMX7ULP/Vybrid to be also a fan of generic
output-enable/input-enable
property.

See:
Figure 5-2. GPIO PAD in Page 241
http://www.nxp.com/assets/documents/data/en/reference-manuals/VFXXXRM.pdf

It has separate register bits to control input buffer enable and
output buffer enable
and we need set it property for GPIO function.

Regards
Dong Aisheng

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#1648333 — Re: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and output-enable

Hi Linus,

On Tue, May 23, 2017 at 06:08:31PM +0800, Dong Aisheng wrote:
> On Tue, May 9, 2017 at 5:19 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Mon, May 8, 2017 at 7:25 PM, jmondi <jacopo@jmondi.org> wrote:
> >
> >> From my perspective these flags are configurations internal to the pin
> >> controller hardware used to enable/disable input buffers when a pin needs to
> >> perform in both direction.
> >> The level of detail I can provide on this is the logical diagram we have pointed
> >> you to already.
> >>
> >> As I assume you are trying to get this answer from us in order to
> >> avoid duplicating things in pin controller sub-system, and I
> >> understand this, but my question here was "can we have those flags as part
> >> of the pinmux property argument list, as that property description
> >> seems to allow us to do that, instead of making them generic pin
> >> configuration properties and upset other developers?"
> >
> > Pinmux with all it's magic flags baked into one is not any better
> > or any more readable. The solution is already very pretty except
> > for these two flags which I am sure we can agree on a way forward
> > for.
> >
> > What we choose between is not this or another less transparent
> > pin configuration mechanism, the mechanism (whether magic bits
> > to pinmux or reasonable properties) does not matter.
> >
> > There is a strong preference to use the generic bindings.
> >
> > So the discussion is whether to use:
> >
> > bi-directional;
> > output-enable;
> >
> > Or some already defined config flags.
> >
> > If these are too idiomatic to be used by others, they should anyways
> > look similar, like:
> >
> > renesas,bi-directional;
> > renesas,output-enable;
> >
> > Like the Qualcomm weirdness found in drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
> >
> > qcom,pull-up-strength = <..>;
> >
> > Check how they use
> > #define PMIC_GPIO_CONF_PULL_UP                 (PIN_CONFIG_END + 1)
> >
> > Etc.
> >
> >> Anyway, I still fail to see why those configuration flags, only
> >> affecting the way the pin controller hardware enables/disables
> >> its internal buffers and its internal operations have to be
> >> described in term of their externally visible electrically characteristics.
> >
> > To me internal vs external is not what matters. What matters is
> > if this is likely to pop up in more platforms, and then the property
> > should be generic.
> >
> > The generic pin config definitions are likely to be picked up by other
> > standards and even be inspiration to hardware engineers so that
> > is why it matters so much.
> >
> >> To me, what already exists are pin configuration properties generic to
> >> the whole pin controller subsystem, and I understand you don't want to
> >> see duplication there.
> >>
> >> At the same time, to me, those flags are settings the pin controller
> >> wants to have specified by software to overcome its hw design flaws,
> >> and are intended to configure its internal buffers in a way it cannot
> >> do by itself for some very specific operation modes (they are listed
> >> in the hw reference manual, it's not something you can chose to
> >> configure or not, if you want a pin working in i2c mode, you HAVE to
> >> pass those flags to pin controller).
> >
> > Sounds like a case for
> >
> > renesas,bi-directional;
> > renesas,output-enable;
> >
> > following the Qualcomm pattern in that case.
> >
> > But let's see if something else comes out of this discussion.
> >
>
> I did not follow too much.
> But it seems IMX7ULP/Vybrid to be also a fan of generic
> output-enable/input-enable
> property.
>
> See:
> Figure 5-2. GPIO PAD in Page 241
> http://www.nxp.com/assets/documents/data/en/reference-manuals/VFXXXRM.pdf
>
> It has separate register bits to control input buffer enable and
> output buffer enable
> and we need set it property for GPIO function.

As it seems we have another user for 'output-enable' here, what if we just
add that one to the generic bindings properties list, and we keep
'bi-directional' (which seems to be the most debated property we have
added) out of generic properties?

We can handle 'bi-directional' pins with static tables in our pin
controller driver and not have it anywhere in DT.

I see commit 42d5a11200d0[1] has not been reverted yet as Andy asked
in some previous email. I can send another version of that patch with
only 'output-enable' if you wish.

Once we reach consesus, I can then send v6 of our pin controller driver
based on that.

Thanks
   j

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8c58f1a7a4b6d1d723bf25fef9d842d5a11200d0
>
> Regards
> Dong Aisheng

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