linux-kernel - Re: [PATCH 3/3] power_supply: max77693: Listen for cable events and enable charging

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Message-id: <298d81d5-fe41-e2d1-32a7-d3dc35b0fe25@kernel.org>
Date:   Wed, 28 Sep 2016 09:56:28 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Wolfgang Wiedmeyer <wolfgit@...dmeyer.de>
Cc:     sre@...nel.org, dbaryshkov@...il.com, dwmw2@...radead.org,
        cw00.choi@...sung.com, b.zolnierkie@...sung.com,
        broonie@...nel.org, lgirdwood@...il.com, lee.jones@...aro.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] power_supply: max77693: Listen for cable events and
 enable charging

On 09/27/2016 03:34 PM, Wolfgang Wiedmeyer wrote:
> 
> Krzysztof Kozlowski writes:
> 
>> On Tue, Sep 27, 2016 at 01:31:10AM +0200, Wolfgang Wiedmeyer wrote:
>>> This patch adds a listener for extcon cable events and enables
>>> charging if an USB cable is connected. It recognizes SDP and DCP cable
>>> types and treats them the same (same input current and fast charge
>>> current). The maximum input current is set before the charger is
>>> enabled and before the charger gets disabled, the maximum input
>>> current is set to zero. The listener is inspired by the listener
>>> implementation that was used for the AXP288 Charger driver.
>>>
>>> The patch also adds support for the CURRENT_NOW property. It reads the
>>> fast charge current that gets set before the charger is enabled or
>>> disabled.
>>>
>>> Signed-off-by: Wolfgang Wiedmeyer <wolfgit@...dmeyer.de>
>>
>> No. This power supply driver should not manage regulators. It is not a
>> regulator consumer. For that specific need, there is a charger-manager driver.
> 
> When I was in the middle of implementing this, I noticed that the
> charger manager does everything that is needed. But it took me quite
> some time to configure the DTS correctly until I realized that the
> charger manager used a deprecated function
> (extcon_register_interest()) and thus couldn't work. And as I didn't see
> the charger-manager in any other device's DTS, I thought that this might
> not be right way.
> But Chanwoo Choi has a fix: https://patchwork.kernel.org/patch/8898541/
> So I will try to get it working with this patch.
> 
>> I agree that you might configure here the charger. You might even expose
>> some writeable properties through power supply class. However the
>> purpose of this driver is to expose the battery charger to user-space,
>> not to replace the user-space with its work.
>>
>> So... NACK.
> 
> Ok, then I will try to reduce the patch to the CURRENT_NOW property
> support.
> 
>> If you would like to play with charger-manager, here is my old DTS for
>> Trats2 (might need updates):
> 
> Is there a reason that this patch is not in the kernel? It would have
> been very helpful for me :)

In general, DeviceTree should describe the hardware. Charger manager is
an abstract device, not a real one. This DT node does not describe real
hardware but it is a driver-specific glue needed to get things done.

I am not convinced that we should add to DTS such abstract devices. What
about people who want to control charging from user-space? They would
have to disable charger-manager from config.

Best regards,
Krzysztof