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SubjectRe: [PATCH] pinctrl: at91-pio4: add support for drive-strength property
On Mon, Jan 29, 2018 at 01:01:30PM -0600, Rob Herring wrote:
> On Mon, Jan 22, 2018 at 09:37:38AM +0100, Linus Walleij wrote:
> > On Thu, Jan 18, 2018 at 5:02 PM, Ludovic Desroches
> > <ludovic.desroches@microchip.com> wrote:
> >
> > > Add support for the drive-strength property. Usually its value is
> > > expressed in mA. Since the numeric value depends on VDDIOP voltage,
> > > the controller uses low, medium and high to define the drive-strengh.
> >
> > Aha I see. That's complex. It certainly results in a certain mA drive
> > strength in the end, but what you're saying is that this is not usually
> > what we configure.
> >
> > > The PIO controller accepts two values for the low drive: 0 or 1. Most
> > > of the time, we don't care about the drive strength, there is no need
> > > to change it, so 0 is considered as the default value.
> >
> > Do you mean default value as in "whatever the hardware was set
> > up as at boot time"?
> >
> > > The low-drive
> > > value won't be advertised through pinconf-pins file excepted if it
> >
> > except?
> >
> > > has been set explicitly in the device tree ie if its value is
> > > different from 0.
> > >
> > > Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
> >
> > OK I think I get it.
> >
> > > Optional properties:
> > > - GENERIC_PINCONFIG: generic pinconfig options to use, bias-disable,
> > > -bias-pull-down, bias-pull-up, drive-open-drain, input-schmitt-enable,
> > > -input-debounce, output-low, output-high.
> > > +bias-pull-down, bias-pull-up, drive-open-drain, drive-strength,
> > > +input-schmitt-enable, input-debounce, output-low, output-high.
> > (...)
> > > + drive-strength = <ATMEL_PIO_DRVSTR_LO>;
> >
> > So you say you support this argument and it will be something like
> >
> > include/dt-bindings/pinctrl/at91.h:#define ATMEL_PIO_DRVSTR_LO 1
> > include/dt-bindings/pinctrl/at91.h:#define ATMEL_PIO_DRVSTR_ME 2
> > include/dt-bindings/pinctrl/at91.h:#define ATMEL_PIO_DRVSTR_HI 3
> >
> > But the definition if generic drive strength is actually in mA.
>
> Yes, and the reason we put unit suffixes on properties is to avoid
> differing units.
>
> > I think it is OK to deviate from stating it in mA, but you should
> > write this in the DT bindings so people do not get confused.
>
> I don't think it is okay. If "drive-strength" doesn't work, then use
> a vendor specific property ("atmel,drive-strength"). Of course, I might
> forget this in the next version and tell you to use a standard property
> in mA.

Ok, so I am going to send the next version! The purpose is to keep using the
generic pinconf parsing function.
If I need to use "atmel,drive-strength" property, I assume I could
manage it with custom_params, isn't it?

Regards

Ludovic

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