linux-kernel - Re: [PATCH] power: bq24261_charger: Add support for TI BQ24261 charger

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Date:	Fri, 11 Sep 2015 09:58:40 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	"Andrew F. Davis" <afd@...com>,
	"Pallala, Ramakrishna" <ramakrishna.pallala@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Sebastian Reichel <sre@...nel.org>,
	"Tc, Jenny" <jenny.tc@...el.com>,
	Andreas Dannenberg <dannenberg@...com>
Subject: Re: [PATCH] power: bq24261_charger: Add support for TI BQ24261 charger

On 11.09.2015 01:42, Andrew F. Davis wrote:
> On 09/09/2015 06:47 PM, Krzysztof Kozlowski wrote:
>>>>> +- ti,enable-user-write: boolean, if present driver will allow the
>>>>> user space
>>>>> +    to control the charging current and voltage through sysfs;
>>>>
>>>> This is not DT property. It does not describe hardware.
>>> We needed a mechanism to enable the sysfs writes on certain properties.
>>> If DT is not the place where should it go?
>>
>> DT is not the place. As I discussed later with Andreas, if you really
>> need this and if mainline is a place for that then probably this should
>> be compile option (a Kconfig symbol).
>>
> 
> I think this would actually be a good use for module parameters, this way
> it could still be set at boot without re-compiling.
> 
> I think compile-time disabling sysfs properties because they are
> "dangerous" is
> a little bit too artificially restricting and controlling, you can set
> permissions
> so only root can change them already. The kernel should not be
> restricting root,
> I understand the fear of someone rooting a machine and remotely over
> charging
> a LiPo[1], but these physical limits are hardware descriptions and can
> and should
> be set by DT, beyond this root should have full control over their machine.


Indeed module parameters could be used for enabling/disabling debug
options... but as fair as I understand these are for purely development
purposes. That is why they got into DT initially, right? To allow the
developer to play with it on the development board?

This is why I am really not convinced that this should go to mainline.

Anyway if it goes, then maybe compiling it out is the safest choice?
What's the purpose of having it in kernel all the time? If this was a
debug option, than some experienced user could turn it on and report to
LKML with extended debug data. But it's not a debug but development option?

> Besides root can already just unbind your driver and issue raw I2C
> commands to do
> the same thing. </rant>
> 
> [1] http://i.imgur.com/vszJJ.jpg

Oh, these weird sickos... That's why I am using IPoAC and always check
the bits by myself for weird looking I2C commands. :)

Best regards,
Krzysztof
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