linux-kernel - Re: [PATCH] mfd: add bq2415x charger driver

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Date:	Tue, 6 Dec 2011 04:49:37 +0200
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Sebastian Reichel <sre@...ian.org>
Cc:	Felipe Contreras <felipe.contreras@...ia.com>,
	linux-main <linux-kernel@...r.kernel.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Pali Rohár <pali.rohar@...il.com>,
	Aliaksei Katovich <aliaksei.katovich@...ia.com>,
	Vladimir Zapolskiy <vz@...ia.com>
Subject: Re: [PATCH] mfd: add bq2415x charger driver

Hi,

2011/12/6 Sebastian Reichel <sre@...ian.org>:
> Good to hear somebody is working on this :) I planned to do this
> myself, but didn't find any time for it. Here are some comments
> from me:

:)

> [...]
>
>> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
>
> I would expect the driver in drivers/power. But maybe MFD is
> better, since the chip can also be used to power USB host?

Perhaps, at least I haven't tried that.

> [...]
>
>> +#define BQ2415X_VOLTAGE_SCALE 20000
>
> If I remember correctly (I read the specs some time ago), this can
> be configured via external resistor. So this is board specific?

Not really. There are 6 bits: 640, 320, 160, 80, 40, 20. So values
from 0 to 1260mV can be represented, at steps of 20mV. A value of 0
means 3.5V.

> [...]
>
>> +     bq2415x_i2c_write(cli, BQ2415X_CHG_CTL, 0x42);
>> +     bq2415x_set_voltage(cli, 0, 4200000);
>> +     bq2415x_set_current_limit(cli, 1800000, 1800000);
>
> So it always charges with 1.8A? Shouldn't this be dependent on the
> input source (e.g. 500mA from USB)? Also what's if no charger is
> connected at all?

No. I'm hard-coding those values, but I wrote the functions
(set_voltate, set_current_limit) so all values are supported.

What is missing is the code to connect this driver to the charger
detector driver (isp1704), so those values are determined dynamically.

> Apart from this I think those values should be exposed to sysfs
> via /sys/class/power_supply.

Perhaps. Although I don't see much of the power supply interface that
could be useful here, but if so, I guess this should be indeed in
'drivers/power'.

Cheers.

-- 
Felipe Contreras
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