Re: bq24735 charger and ac-detect

[Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On 14/12/16 21:22, Peter Rosin wrote:
> On 2016-12-14 18:54, Jon Hunter wrote:

...

>> Hmmm ... looking closer at the schematics I see a power-MOSFET in the
>> path of the ACOK to the Tegra and it looks like this could be inverting
>> the signal! Seems this was not caught when the code was submitted. This
>> should have been described in the device-tree somewhere :-(
> 
> That's what I suspected...
> 
> Ok, I expect the ship has sailed and that it's too late to actually fix
> this up with active-low in various Tegra dts files and removing the negation
> in the code, without causing ripples and regressions? Because that would
> be the clean fix!

Yes, unfortunately it has sailed as we cannot break compatibility AFAIK.
However, that said, I am not 100% certain for cases where there is a bug
like this.

I did double check this morning and verified that the gpio is low when
the charger is connected and so it is inverted.

> One other thing to possibly do is add a new binding that is not negated,
> and perhaps named after the pin in the data-sheet, i.e. ti,acok-gpios,
> and deprecate ti,ac-detect-gpios. But that's no fun as it leaves a bunch of
> compat code that wastes space and some lucky person has to maintain it.
> 
> Perhaps the best thing to do is to just re-document ti,ac-detect-gpios
> to be the inverse of what is currently described, i.e. to be AC absence
> instead of AC presence? But that feels like giving up and it isn't really
> nice from a device-tree point of view either, but I guess those points are
> fairly accademic? Or are there any non-Linux users of this binding? How are
> these things handled when they pop up elsewhere?

I guess that ideally the polarity should have been specified correctly
by the gpio property, but even this looks wrong for Tegra as it is
GPIO_ACTIVE_HIGH and not LOW. The only other option is to add another
property called something like 'ti,ac-detect-override-pol' to specify
the polarity you want.

To be honest, I am not sure how this type of thing is normally handled.
So probably best to put together a patch with whatever option you feel
best and explain why this is needed and see what the dev-tree folks say.

Cheers
Jon

-- 
nvpublic