Re: [RFI] pinmux: pin group ownership

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Tue, May 12, 2015 at 1:53 PM, Jon Hunter <jonathanh@xxxxxxxxxx> wrote:

[Me]:
>> The usecount are done on individual pins, not groups.
>
> Thanks for confirming. With regard to the change
> e5b3b2d9ed202697a937c282f9c4d93b1e3e0848, IIUC then this allows devices
> not to define any pins but just groups. Probably because from some
> devices (such as berlin) pinmux'ing is always done at the group level.

That's correct.

> If this is the case then it would appear that there is no protection
> against two devices trying to use the same group. Is this correct?

Seems like so... darn you found a loophole.

>> In the devel tree you can even set the pinmux_ops.strict to disallow
>> GPIOs and other functions to share a pin.
>
> Thanks, however, I don't think that this helps in this case because
> pin_request() would not be called by pinmux_enable_setting() as num_pins
> = 0.

You're right.

The implementation assumes collissions happen at pin level,
not group level.

I wonder if there are enough devices out there with this problem
that we need to check for it?

If so I would opt to create a bool .group_only property
on pinmux_ops like we created .strict so that we can
avoid all pin-specific code on such pin controllers.

But I don't know it it's worth it for these few pin controllers :/

On the U300 there is only group selection, but the datasheet
helpfully defined all pins anyway so I could handle collissions
on the pin level. This is the ideal solution if possible.

Yours,
Linus Walleij
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