linux-kernel - Re: [PATCH v2] mfd: tps65910: Correct power-off programming sequence

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Date:   Tue, 26 May 2020 17:01:01 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Tony Lindgren <tony@...mide.com>, Lee Jones <lee.jones@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Zack Pearsall <zpearsall@...oo.com>,
        linux-tegra@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mfd: tps65910: Correct power-off programming sequence

On Sun, May 24, 2020 at 10:26:43PM +0300, Dmitry Osipenko wrote:
> This patch fixes system shutdown on a devices that use TPS65910 as a
> system's power controller. In accordance to the TPS65910 datasheet, the
> PMIC's state-machine transitions into the OFF state only when DEV_OFF
> bit of DEVCTRL_REG is set. The ON / SLEEP states also should be cleared,
> otherwise PMIC won't get into a proper state on shutdown. Devices like
> Nexus 7 tablet and Ouya game console are now shutting down properly.

The datasheets of 65910 and 65911 say that ON and SLP bits are cleared
during OFF state. But I guess the hardware might work differently.

[...]
> --- a/drivers/mfd/tps65910.c
> +++ b/drivers/mfd/tps65910.c
> @@ -440,8 +440,13 @@ static void tps65910_power_off(void)
>  			DEVCTRL_PWR_OFF_MASK) < 0)
>  		return;
>  
> -	tps65910_reg_clear_bits(tps65910, TPS65910_DEVCTRL,
> -			DEVCTRL_DEV_ON_MASK);
> +	if (tps65910_reg_clear_bits(tps65910, TPS65910_DEVCTRL,
> +			DEVCTRL_DEV_SLP_MASK) < 0)
> +		return;
> +
> +	tps65910_reg_update_bits(tps65910, TPS65910_DEVCTRL,
> +				 DEVCTRL_DEV_OFF_MASK | DEVCTRL_DEV_ON_MASK,
> +				 DEVCTRL_DEV_OFF_MASK);
>  }

There is tps65910_reg_set_bits() at the start of function. I guess it
doesn't work if your changes are needed. Maybe you can remove it?

I would also include your observations about the chip's behaviour in the
commit message so it doesn't get "fixed" later.

Best Regards,
Michał Mirosław