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

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Message-id: <e9c76587-1a50-167c-0f4b-2442cbc0fa39@kernel.org>
Date:   Wed, 28 Sep 2016 10:04:41 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Wolfgang Wiedmeyer <wolfgit@...dmeyer.de>,
        Mark Brown <broonie@...nel.org>
Cc:     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

On 09/27/2016 07:51 PM, Wolfgang Wiedmeyer wrote:
> 
> 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?

Yes, reading from this register will give only information about
currently set charge current. Not the real current.

Best regards,
Krzysztof