linux-kernel - Re: [PATCH] power_supply: support CHARGE

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Message-ID: <20080508130102.3218f1e9@ephemeral>
Date:	Thu, 8 May 2008 13:01:02 -0400
From:	Andres Salomon <dilinger@...ued.net>
To:	avorontsov@...mvista.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>, cbou@...l.ru,
	linux-kernel@...r.kernel.org, dwmw2@...radead.org,
	richard@...top.org
Subject: Re: [PATCH] power_supply: support CHARGE_NOW in OLPC battery

Ok, CC'ing Richard as I should've done in the first place...



On Thu, 8 May 2008 14:51:45 +0400
Anton Vorontsov <avorontsov@...mvista.com> wrote:

> On Thu, May 08, 2008 at 12:34:54AM -0400, Andres Salomon wrote:
> > 
> > This is originally based on a patch by
> > David Woodhouse <dwmw2@...radead.org>.  Add support for
> > PROP_CHARGE_NOW by querying the ACR (accumulated current register)
> > from the EC.
> > 
> > Signed-off-by: Andres Salomon <dilinger@...ian.org>
> > ---
> 
> Hi Andres,
> 
> >  drivers/power/olpc_battery.c |   10 +++++++++-
> >  1 files changed, 9 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/power/olpc_battery.c
> > b/drivers/power/olpc_battery.c index e3f6ec8..517dacd 100644
> > --- a/drivers/power/olpc_battery.c
> > +++ b/drivers/power/olpc_battery.c
> > @@ -19,7 +19,7 @@
> >  
> >  #define EC_BAT_VOLTAGE	0x10	/* uint16_t,
> > *9.76/32,    mV   */ #define EC_BAT_CURRENT	0x11	/*
> > int16_t,	*15.625/120, mA   */ -#define EC_BAT_ACR	0x12
> > +#define EC_BAT_ACR	0x12	/* int16_t,
> > *416.667,    µAh  */
> 
> The hardware reports uAh * 416.667..?

Perhaps.  Richard informs me that this might be incorrect.  Richard,
would you care to clarify exactly what the ACR register value
contains?  It sounds like we can't get uAh without taking two reads over
time and computing them.

Bonus points if one of us remembers to update
http://wiki.laptop.org/go/Ec_specification with the information. :)

The code snippet above is mangled due to wrapping.  It was originally:

-#define EC_BAT_ACR     0x12
+#define EC_BAT_ACR     0x12    /* int16_t,     *416.667,    µAh  */



> 
> >  #define EC_BAT_TEMP	0x13	/* uint16_t,
> > *100/256,   °C  */ #define EC_AMB_TEMP	0x14	/*
> > uint16_t,	*100/256,   °C  */ #define EC_BAT_STATUS
> > 0x15	/* uint8_t,	bitmask */ @@ -289,6 +289,13 @@
> > static int olpc_bat_get_property(struct power_supply *psy, ec_word
> > = be16_to_cpu(ec_word); val->intval = ec_word * 100 / 256;
> >  		break;
> > +	case POWER_SUPPLY_PROP_CHARGE_NOW:
> > +		ret = olpc_ec_cmd(EC_BAT_ACR, NULL, 0, (void
> > *)&ec_word, 2);
> > +		if (ret)
> > +			return ret;
> > +
> > +		val->intval = be16_to_cpu(ec_word);
> 
> But you didn't convert it to the uAh, I think you should.


We have logic in userspace that converts ACR to a useful number; for
our purposes, we'd just like to read the raw ACR values.

Perhaps CHARGE_NOW is the wrong thing to be using, if we can't get
uAh and CHARGE_* requires that unit.


> 
> > +		break;
> >  	case POWER_SUPPLY_PROP_SERIAL_NUMBER:
> >  		ret = olpc_ec_cmd(EC_BAT_SERIAL, NULL, 0, (void
> > *)&ser_buf, 8); if (ret)
> > @@ -317,6 +324,7 @@ static enum power_supply_property
> > olpc_bat_props[] = { POWER_SUPPLY_PROP_TEMP_AMBIENT,
> >  	POWER_SUPPLY_PROP_MANUFACTURER,
> >  	POWER_SUPPLY_PROP_SERIAL_NUMBER,
> > +	POWER_SUPPLY_PROP_CHARGE_NOW,
> >  };
> >  
> >  /* EEPROM reading goes completely around the power_supply API,
> > sadly */
> 
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