linux-kernel - Re: [PATCH v3 2/4] mfd: add Gateworks System Controller core driver

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Date:   Tue, 3 Apr 2018 08:48:27 -0700
From:   Tim Harvey <tharvey@...eworks.com>
To:     Lee Jones <lee.jones@...aro.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Wim Van Sebroeck <wim@...ana.be>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-hwmon@...r.kernel.org,
        linux-input@...r.kernel.org, linux-watchdog@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v3 2/4] mfd: add Gateworks System Controller core driver

On Wed, Mar 28, 2018 at 8:14 AM, Tim Harvey <tharvey@...eworks.com> wrote:
> The Gateworks System Controller (GSC) is an I2C slave controller
> implemented with an MSP430 micro-controller whose firmware embeds the
> following features:
>  - I/O expander (16 GPIO's) using PCA955x protocol
>  - Real Time Clock using DS1672 protocol
>  - User EEPROM using AT24 protocol
>  - HWMON using custom protocol
>  - Interrupt controller with tamper detect, user pushbotton
>  - Watchdog controller capable of full board power-cycle
>  - Power Control capable of full board power-cycle
>
> see http://trac.gateworks.com/wiki/gsc for more details
>
<snip>
> +
> +/*
> + * gsc_powerdown - API to use GSC to power down board for a specific time
> + *
> + * secs - number of seconds to remain powered off
> + */
> +static int gsc_powerdown(struct gsc_dev *gsc, unsigned long secs)
> +{
> +       int ret;
> +       unsigned char regs[4];
> +
> +       dev_info(&gsc->i2c->dev, "GSC powerdown for %ld seconds\n",
> +                secs);
> +       regs[0] = secs & 0xff;
> +       regs[1] = (secs >> 8) & 0xff;
> +       regs[2] = (secs >> 16) & 0xff;
> +       regs[3] = (secs >> 24) & 0xff;
> +       ret = regmap_bulk_write(gsc->regmap, GSC_TIME_ADD, regs, 4);
> +
> +       return ret;
> +}

Any feedback on the 'powerdown' sysfs attribute that hooks to this
function? This allows the GSC to disable the board primary power
supply for 2^32 seconds and is often used to 'reset' the board
although it could also be used to put the board in a power down state
longer. I'm wondering if there is a more appropriate API for this in
the kernel that I don't know about.

I would also like to register a restart handler using this but I
believe that ARM restart handlers currently can not use I2C - is that
correct?

Regards,

Tim