Re: [RFI] pinmux: pin group ownership

[Jon Hunter <jonathanh@nvidia.com>]

On 12/05/15 13:10, Linus Walleij wrote:
> On Tue, May 12, 2015 at 1:53 PM, Jon Hunter <jonathanh@nvidia.com> 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.

Ok, I was hoping I had missed something, so thanks for confirming.

>>> 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?

Probably not many, indeed.

> 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.

Yes, I agree registering all pins would be ideal, however, I could see
that this may seem unnecessary for some devices.

Thanks for the info.

Cheers
Jon

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