linux-kernel - RE: [PATCH v2 1/2] mfd: da9062: enable being a system-power-controller

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Message-ID: <OSAPR01MB5060E32302F81F37D17B08A2B0FB9@OSAPR01MB5060.jpnprd01.prod.outlook.com>
Date:   Tue, 26 Apr 2022 09:14:34 +0000
From:   DLG Adam Thomson <DLG-Adam.Thomson.Opensource@...renesas.com>
To:     Helmut Grohne <helmut.grohne@...enta.de>,
        Support Opensource <Support.Opensource@...semi.com>,
        Lee Jones <lee.jones@...aro.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        DLG Adam Thomson <DLG-Adam.Thomson.Opensource@...renesas.com>,
        Mark Brown <broonie@...nel.org>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: RE: [PATCH v2 1/2] mfd: da9062: enable being a
 system-power-controller

On 22 April 2022 07:17, Helmut Grohne wrote:

> The DA9062 can be the device used to power the CPU. In that case, it can
> be used to power off the system. In the CONTROL_A register, the M_*_EN
> bits must be zero for the corresponding *_EN bits to have an effect. We
> zero them all to turn off the system.
> 
> Signed-off-by: Helmut Grohne <helmut.grohne@...enta.de>
> ---
>  drivers/mfd/da9062-core.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> This series effectively is a rebased resend. The earlier posting was
> https://lore.kernel.org/all/20200107120559.GA700@laureti-dev/. At that time,
> Adam Thomson critisized the use of regmap and i2c inside a pm_power_off hook
> since irqs are disabled. He reached out to Lee Jones, who asked Mark Brown and
> Wolfram Sang, but never got any reply. I noted that a fair number of other
> drivers do use regmap and i2c despite this issue. In the mean time, more
> instances were added:
>  * drivers/mfd/acer-ec-a500.c uses i2c
>  * drivers/mfd/ntxec.c uses i2c
>  * drivers/mfd/rk808.c uses regmap and i2c
> Given that we proceeded with accepting the use of i2c and regmap inside
> pm_power_off hooks, I think we can proceed with this patch as well.
> 
> Helmut

I still have concerns, but maybe it's up to the integrator of a platform to
determine if this approach for poweroff is valid and usable, although I still
think it would be good to have checks somewhere as to whether a platform can
actually perform atmoic I2C access when IRQs are disabled. However, without
further insight right now:

Reviewed-by: Adam Thomson <DLG-Adam.Thomson.Opensource@...renesas.com>