linux-kernel - Re: bq24190: What's the correct API to turn boost mode (OTG) on for the battery charger ?

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Message-ID: <1782446.TpztL69o3V@avalon>
Date:	Fri, 16 May 2014 00:35:34 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	"Mark A. Greer" <mgreer@...malcreek.com>
Cc:	linux-kernel@...r.kernel.org,
	David Woodhouse <dwmw2@...radead.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Anton Vorontsov <anton@...msg.org>
Subject: Re: bq24190: What's the correct API to turn boost mode (OTG) on for the battery charger ?

Hi Mark,

Thank you for the quick reply.

On Thursday 15 May 2014 15:08:44 Mark A. Greer wrote:
> On Thu, May 15, 2014 at 10:29:26PM +0200, Laurent Pinchart wrote:
> > Hello,
> 
> [Adding Anton Vorontsov to CC list.]
> 
> Hi Laurent.
> 
> > I'm trying to enable battery charging on an OMAP4 board based on a twl6030
> > PMIC with external bq24190 battery charger and bq27510 fuel gauge.
> > 
> > The system has an OTG USB port that can be used to charge the battery, and
> > that can also be used in host mode. In that case the bq24190 needs to be
> > switched to boost mode to provide the +5V power supply from the battery.
> > 
> > The bq24190 has a charge configuration register field that supports charge
> > disabled, charge enabled and OTG (boost mode). The field is set by the
> > bq24190 driver in response to setting the charge type :
> > POWER_SUPPLY_CHARGE_TYPE_NONE will disable charing, and
> > POWER_SUPPLY_CHARGE_TYPE_TRICKLE and
> > POWER_SUPPLY_CHARGE_TYPE_FAST will enable it. However, OTG boost mode is
> > not supported.
> > 
> > 
> > The driver exposes most register fields as sysfs attributes (which doesn't
> > sound very safe to me, but that's another story). I can thus enable OTG
> > boost mode directly from userspace through the driver-specific API, but
> > that just bypasses the power supply API. I'm thus not very fond of that
> > solution.
>
> No, its not a good solution.  As indicated in the commit log, the sysfs
> entries are there because there are just so many fields that don't map
> well to the existing interface.
> 
> Maybe we should add support for a DT entry to enable exporting those
> fields(disabled by default)?
> 
> > Possibly due to my really basic (not to say nonexistent) knowledge of the
> > power supply subsystem I haven't found an API to expose this feature. I
> > was wondering if someone had given a though regarding how to implement
> > this properly.
> 
> What if we just added something like POWER_SUPPLY_CHARGE_TYPE_BOOST?

That was actually my first thought, and I assumed it would be rejected as 
boost mode is not a charge type but a discharge type :-) This being said, I 
don't have enough experience with battery chargers to decide whether this is a 
good solution. If you believe it is, I'll trust you on that.

On a side note, is there any reference userspace implementation of a battery 
manager ? The vendor BSP I've received with the board hardcodes calls to the 
bq24190 in the MUSB driver to switch between OTG and trickle charge modes 
based on USB cable connection/disconnection events. That's pretty ugly, and I 
assume this should be handled in userspace - or is there a standard kernel 
infrastructure for that ? 

-- 
Regards,

Laurent Pinchart

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