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 [off-list ref] wrote:

quoted

On Mon, May 8, 2017 at 7:25 PM, jmondi [off-list ref] wrote:

quoted

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.

quoted

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.

quoted

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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