linux-kernel - Re: [RESEND PATCH v3 3/3] regulator: mcp16502: add regulator driver for MCP16502

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Date:   Thu, 13 Dec 2018 12:19:16 +0000
From:   <Andrei.Stefanescu@...rochip.com>
To:     <broonie@...nel.org>
CC:     <robh+dt@...nel.org>, <lgirdwood@...il.com>,
        <mark.rutland@....com>, <gregkh@...uxfoundation.org>,
        <Cristian.Birsan@...rochip.com>, <Nicolas.Ferre@...rochip.com>,
        <Claudiu.Beznea@...rochip.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <andr3i.stefanescu@...il.com>
Subject: Re: [RESEND PATCH v3 3/3] regulator: mcp16502: add regulator driver
 for MCP16502

Hi Mark,

On 12.12.2018 17:55, Mark Brown wrote:
> On Wed, Dec 12, 2018 at 08:01:07AM +0000, Andrei.Stefanescu@...rochip.com wrote:
>
>>> This puts the device into low power mode when the suspend function gets
>>> called but this might not be safe - devices using the regulator may not
>>> be suspended yet so could still need full regulation.  Normally a GPIO
>>> triggered transition like this would be being done by hardware as part
>>> of the process of suspending the SoC.  Is there some reason to do this
>>> manually?
>> There is a line from the MPU (SHDN) which goes low only when the MPU
>> turns off. That line is already connected to the PMIC and it differentiates
>> between suspend-to-mem and standby. To switch to low-power, the PMIC must
>> be controlled by the GPIO pin LPM.
>> The suspend sequence is:
>> - LPM pin goes high (PMIC enters Low-Power <-> Linux standby)
>> - SHDN goes low (if target suspend state is mem) and then PMIC enters
>> HIBERNATE
> This feels like it should be being controlled somewhere else, if it's
> actually causing a change in the PMIC state it seems like it wants to be
> done as late as possible in suspend to minimize the risks.  At the very
> least suspend_late() for the driver seems appropriate.
I tried with both suspend_late/resume_early and suspend_noirq/resume_noirq.
Everything seems to work ok.

Which one do you think is more appropriate? I am guessing that during
suspend_late some devices may still need to be turned on and that it would
be the safest during suspend_noirq.

Note: the GPIO pin used for LPM is a special one (it maintains its 
voltage during
suspend-to-mem). It is part of the SoC and its methods for setting the 
values
do not sleep.

>
> Could you submit a version with this feature at least split out into a
> separate patch please so we can apply the rest of the code while this is
> discussed?
Sent one patch series and another patch with the current suspend/resume
implementation.

Best regards,
Andrei