Re: [PATCH v2 2/5] devicetree: power: Add docs for TI BQ24190 battery charger

[Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>]

* Liam Breck <liam-RYWXG+zxWwBdeoIcmNTgJF6hYfS7NtTn@public.gmane.org> [170816 13:11]:
> On Wed, Aug 16, 2017 at 8:47 AM, Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org> wrote:
> > * Liam Breck <liam-RYWXG+zxWwBdeoIcmNTgJF6hYfS7NtTn@public.gmane.org> [170812 12:00]:
> >> On Sat, Aug 12, 2017 at 9:42 AM, Sebastian Reichel <sre-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> >> > On Fri, Aug 11, 2017 at 02:57:10PM -0700, Liam Breck wrote:
> >> >> >> +Other features:
> >> >> >> +- Use gpio-hog to set the OTG pin high to enable 500mA charge current on USB SDP port.
> >> >> >
> >> >> > Why doesn't the charger driver control this?
> >> >>
> >> >> This pin/gpio has to be high when USB is plugged in to make the
> >> >> charger chip negotiate 500mA from a SDP port. It should generally be
> >> >> configured that way even if the driver is not loaded, as the chip does
> >> >> not require a driver to function. Some boards may do that with a
> >> >> pull-up. Also the user may want to change this via sysfs and not have
> >> >> the driver "fix" it.
> >> >
> >> > drivers/power/supply/qcom_smbb.c exposes the otg feature as
> >> > regulator. I think in this case it could be exposed as
> >> > gpio-regulator.
> >>
> >> Hans is doing that here:
> >> https://patchwork.kernel.org/patch/9883717/
> >>
> >> The datasheet labels one pin "OTG" but that's misleading; it really
> >> enables negotiation of 500mA input current, but does not turn on OTG
> >> mode. If this pin is low, it only prevents the driver from starting
> >> OTG mode via I2C msg.
> >
> > Yeah so before the device has enumerated this pin keeps the
> > max current at 100mA as required by the USB spec. This pin
> > should be only toggled after enumerating in bootloader or
> > by the kernel driver. I tink the USB PHY driver can also
> > be wired to control this line.
> >
> > Probably best to set it up as just a GPIO that the bq24190
> > driver controls optionally.
> >
> > Then later on we should have some Linux generic way for
> > USB gadget subsystem to tell the charger that we have
> > enumerated, and then bq24190 driver can toggle this GPIO
> > to enable higher charge rates.
> 
> I discovered a few months ago that setting this pin high after USB
> connect has NO effect on iinlim. It has to be high at connect to
> auto-negotiate 500mA. There is no point in making the driver control
> this pin; we already tried that.
> 
> Here we are just documenting how the DT can enable this pin via gpio-hog.

Or in bootloader. Yeah this is mostly for completely empty
battery to start charging at 100mA until bootloader can start
and enable higher rates.

> I believe the only way to defer 500mA negotiation is to leave this pin
> off and set iinlim via I2C msg to chip. We can do that in a gadget
> script via sysfs input_current_limit. Hans does not have to enable
> this pin to start OTG-host on his x86 device, perhaps because it is
> wired high there. Our script can set the linked gpio high if nec for
> OTG-host.

Yeah once something is running?

If the kernel does not need to do anything about it, how about
just leave it out of the binding docs then?

Regards,

Tony
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