Re: [PATCH] usb: dwc3: fix build error when POWER_SUPPLY is not enabled

[Ray Chi <raychi@google.com>]

Hi Sebastian,

Sorry for the late reply.

On Wed, Mar 10, 2021 at 2:58 AM Sebastian Reichel <sre@kernel.org> wrote:
>
> Hi,
>
> On Mon, Mar 08, 2021 at 09:31:46PM +0800, Ray Chi wrote:
> > Fix build error when CONFIG_POWER_SUPPLY is not enabled.
> >
> > The build error occurs in mips (cavium_octeon_defconfig).
> >
> > mips-linux-gnu-ld: drivers/usb/dwc3/core.o: in function `dwc3_remove':
> > drivers/usb/dwc3/core.c:1657: undefined reference to `power_supply_put'
> > mips-linux-gnu-ld: drivers/usb/dwc3/core.o: in function `dwc3_get_properties':
> > drivers/usb/dwc3/core.c:1270: undefined reference to `power_supply_get_by_name'
> > mips-linux-gnu-ld: drivers/usb/dwc3/core.o: in function `dwc3_probe':
> > drivers/usb/dwc3/core.c:1632: undefined reference to `power_supply_put'
> >
> > Fixes: 59fa3def35de ("usb: dwc3: add a power supply for current control")
> > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> > Signed-off-by: Ray Chi <raychi@google.com>
> > ---
>
> While I'm fine with merging this after fixing up the subject, the
> original patch for dwc3 [0] looks completly incorrect to me.
>
> First of all it uses wrong scale (power-supply uses uA, not mA),
> so you are charging 1000x slower than expected. Then the patchset
> introduces a new DT property to get the power-supply device, but
> does not update the DT binding documentation and does not Cc the
> DT binding maintainer.

Yes, it should use uA and send this information, and I will update a
patch to fix it and add the DT binding documentation.

> Next the property itself looks not very
> smart to me. Usually one would use a device reference, not the
> Linux device name.
>
> Finally all existing devices solve this by registering a usb
> notifier from the charger, so why are you going the other way
> around? This is going to break once you want to use one of the
> existing chargers with dwc3.

Only the USB controller will know USB state/speed so that I think it is
better to send this information from the USB side.
For example:
For USB high speed, charging current should be limited to 500 mA in
configured state.
For USB super speed, charging current should be limited to 900 mA in
configured state.

>
> I suggest to drop/revert the whole patchset.
>
> [0] https://lore.kernel.org/linux-usb/20210222115149.3606776-1-raychi@google.com/
>
> -- Sebastian
>
> >  include/linux/power_supply.h | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
> > index 81a55e974feb..6e776be5bfa0 100644
> > --- a/include/linux/power_supply.h
> > +++ b/include/linux/power_supply.h
> > @@ -381,8 +381,14 @@ struct power_supply_battery_info {
> >  extern struct atomic_notifier_head power_supply_notifier;
> >  extern int power_supply_reg_notifier(struct notifier_block *nb);
> >  extern void power_supply_unreg_notifier(struct notifier_block *nb);
> > +#if IS_ENABLED(CONFIG_POWER_SUPPLY)
> >  extern struct power_supply *power_supply_get_by_name(const char *name);
> >  extern void power_supply_put(struct power_supply *psy);
> > +#else
> > +static inline void power_supply_put(struct power_supply *psy) {}
> > +static inline struct power_supply *power_supply_get_by_name(const char *name)
> > +{ return NULL; }
> > +#endif
> >  #ifdef CONFIG_OF
> >  extern struct power_supply *power_supply_get_by_phandle(struct device_node *np,
> >                                                       const char *property);
> > --
> > 2.30.1.766.gb4fecdf3b7-goog
> >