linux-kernel - Re: [PATCH 2/3] regulator: max77693: Also manipulate the fast charge current

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Message-ID: <874m51w7r7.fsf@machinist.wiedmeyer.de>
Date:   Tue, 27 Sep 2016 19:51:56 +0200
From:   Wolfgang Wiedmeyer <wolfgit@...dmeyer.de>
To:     Mark Brown <broonie@...nel.org>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>, sre@...nel.org,
        dbaryshkov@...il.com, dwmw2@...radead.org, cw00.choi@...sung.com,
        b.zolnierkie@...sung.com, lgirdwood@...il.com,
        lee.jones@...aro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] regulator: max77693: Also manipulate the fast charge current


Mark Brown writes:

> On Tue, Sep 27, 2016 at 03:50:42PM +0200, Wolfgang Wiedmeyer wrote:
>
>> When charging is disabled (e.g. by removing the USB cable) the charge
>> current is not reset to zero. So if I expose the current by the
>> CURRENT_NOW property, it incorrectly reports the current that was set
>> when charging was enabled, although there is no charging going on
>> anymore. So I felt the need to update the charge current every time the
>> charger gets enabled or disabled.
>> Initially, the charge current is set to zero, so I think it needs to be
>> set at least at the beginning to enable charging.
>
> Are you sure that the register value you're looking at is the actual
> charge current right now and not just the maximum that the charger will
> try to use depending on the conditions (supply available, battery
> state...)?  It seems like you're acting as though it's the latter but
> that's not what the chip is doing.

I was looking at the vendor code that was released for the Galaxy S3 and
there the same register gets accessed for getting the current for
the CURRENT_NOW property [1] and for setting the current [2]. So is this
probably the wrong use of the CURRENT_NOW property because not the
actual charge current is read but the maximum value that was
set? Unfortunately, I don't have access to the datasheet and I didn't
find it online so I don't know where the actual current can be
accessed.

Thanks,
Wolfgang

[1] https://code.fossencdi.org/kernel_samsung_smdk4412.git/tree/drivers/battery/max77693_charger.c#n531

[2] https://code.fossencdi.org/kernel_samsung_smdk4412.git/tree/drivers/battery/max77693_charger.c#n552

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