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

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Date:   Thu, 23 Jan 2020 15:51:37 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.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>
Subject: RE: [PATCH 1/2] mfd: da9062: enable being a system-power-controller

On 07 January 2020 12:06, 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 patch includes the functionality into the da9062-core driver. If
> that is not the preferred way to integrate it, it can be added as a
> mfd_cell instead. In that case, I can move the functionality to a new
> drivers/power/reset/da9062-poweroff.c. As far as I can see, doing so
> implies that we can no longer use the standard system-power-controller
> property though and must use a new compatible property
> dlg,da9062-poweroff. Please let me know your preference.

I have concerns about using regmap/I2C within the pm_power_off() callback
function although I am aware there are other examples of this in the kernel. At
the point that is called I believe IRQs are disabled so it would require a
platform to have an atomic version of the I2C bus's xfer function. Don't know
if there's a check to see if the bus supports this, but if not then maybe it's
something worth adding? That way we can then only support the pm_power_off()
approach on systems which can actually do it.

> 
> diff --git a/drivers/mfd/da9062-core.c b/drivers/mfd/da9062-core.c
> index e69626867c26..a2b5dfee677f 100644
> --- a/drivers/mfd/da9062-core.c
> +++ b/drivers/mfd/da9062-core.c
> @@ -572,6 +572,23 @@ static const struct of_device_id da9062_dt_ids[] = {
>  };
>  MODULE_DEVICE_TABLE(of, da9062_dt_ids);
> 
> +/* Hold client since pm_power_off is global. */
> +static struct i2c_client *da9062_i2c_client;
> +
> +static void da9062_power_off(void)
> +{
> +	struct da9062 *chip = i2c_get_clientdata(da9062_i2c_client);
> +	const unsigned int mask = DA9062AA_SYSTEM_EN_MASK |
> +		DA9062AA_POWER_EN_MASK | DA9062AA_POWER1_EN_MASK
> |
> +		DA9062AA_M_SYSTEM_EN_MASK |
> DA9062AA_M_POWER_EN_MASK |
> +		DA9062AA_M_POWER1_EN_MASK;
> +	int ret = regmap_update_bits(chip->regmap, DA9062AA_CONTROL_A,
> mask, 0);
> +
> +	if (ret < 0)
> +		dev_err(&da9062_i2c_client->dev,
> +			"DA9062AA_CONTROL_A update failed, %d\n", ret);
> +}
> +
>  static int da9062_i2c_probe(struct i2c_client *i2c,
>  	const struct i2c_device_id *id)
>  {
> @@ -661,6 +678,15 @@ static int da9062_i2c_probe(struct i2c_client *i2c,
>  		return ret;
>  	}
> 
> +	if (of_device_is_system_power_controller(i2c->dev.of_node)) {
> +		if (!pm_power_off) {
> +			da9062_i2c_client = i2c;
> +			pm_power_off = da9062_power_off;
> +		} else {
> +			dev_warn(&i2c->dev, "Poweroff callback already
> assigned\n");
> +		}
> +	}
> +
>  	return ret;
>  }
> 
> @@ -668,6 +694,11 @@ static int da9062_i2c_remove(struct i2c_client *i2c)
>  {
>  	struct da9062 *chip = i2c_get_clientdata(i2c);
> 
> +	if (pm_power_off == da9062_power_off)
> +		pm_power_off = NULL;
> +	if (da9062_i2c_client)
> +		da9062_i2c_client = NULL;
> +
>  	mfd_remove_devices(chip->dev);
>  	regmap_del_irq_chip(i2c->irq, chip->regmap_irq);
> 
> --
> 2.20.1