linux-kernel - Re: [Regulator] Request for clarification - GPIO controlled regulator, USB VBUS,

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Date:   Wed, 4 Oct 2017 12:45:39 +0200
From:   Łukasz Majewski <l.majewski@...ess.pl>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-input@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [Regulator] Request for clarification - GPIO controlled
 regulator, USB VBUS,

Hi Mark,

Thank you for your reply.

> On Tue, Oct 03, 2017 at 06:58:00PM +0200, Łukasz Majewski wrote:
> 
>> Have I overlooked something? Maybe there is any other mainline code, which I
>> could reuse?
> 
> No, we don't support randomly toggling power for devices without their
> cooperation - it's not generally going to end well.  The reason it's
> difficult to do this is that it's a bad idea.

I do understand the rationale. No issues with this.

>  Perhaps this is something
> that could be implemented generically for USB as it's a hotpluggable bus

In this case we use VBUS as a power supply voltage. The problem with 
regulator API used in this case is that we enable it on boot-up, but 
then we cannot "symulate hotplug" anymore.

> but I'm not convinced.
> 

Maybe, I can look into USB driver and see if the VBUS is manageable from 
there (so I could add some sysfs entry to control it if needed).

-- 
Best regards.

Łukasz Majewski