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From:   "Jonas Mark (BT-FIR/ENG1-Grb)" <Mark.Jonas@de.bosch.com>
To:     Adam Thomson <Adam.Thomson.Opensource@diasemi.com>,
        Support Opensource <Support.Opensource@diasemi.com>,
        Lee Jones <lee.jones@linaro.org>,
        "Rob Herring" <robh+dt@kernel.org>
CC:     "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
        Steve Twiss <stwiss.opensource@diasemi.com>,
        "marek.vasut@gmail.com" <marek.vasut@gmail.com>,
        "RUAN Tingquan (BT-FIR/ENG1-Zhu)" <Tingquan.Ruan@cn.bosch.com>,
        "Streidl Hubert (BT-FIR/ENG1-Grb)" <Hubert.Streidl@de.bosch.com>,
        "Jonas Mark (BT-FIR/ENG1-Grb)" <Mark.Jonas@de.bosch.com>,
        "festevam@gmail.com" <festevam@gmail.com>,
        "o.rempel@pengutronix.de" <o.rempel@pengutronix.de>,
        "anson.huang@nxp.com" <anson.huang@nxp.com>
Subject: AW: [PATCH 1/1] mfd: da9063: Support SMBus and I2C mode
Thread-Topic: [PATCH 1/1] mfd: da9063: Support SMBus and I2C mode
Thread-Index: AQHW8xlUd4non6+XsUm+Dh7IRb1SI6o9EwMAgAAgDYA=
Date:   Thu, 28 Jan 2021 16:09:56 +0000
Message-ID: <df52d5e7069541e78b8b01ddc54a6777@de.bosch.com>
References: <20210125125458.1302525-1-mark.jonas@de.bosch.com>
 <20210125125458.1302525-2-mark.jonas@de.bosch.com>
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Hi Adam,

> > From: Hubert Streidl <hubert.streidl@de.bosch.com>
> >
> > By default the PMIC DA9063 2-wire interface is SMBus compliant. This
> > means the PMIC will automatically reset the interface when the clock
> > signal ceases for more than the SMBus timeout of 35 ms.
> >
> > If the I2C driver / device is not capable of creating atomic I2C
> > transactions, a context change can cause a ceasing of the the clock
> > signal. This can happen if for example a real-time thread is scheduled.
> > Then the DA9063 in SMBus mode will reset the 2-wire interface.
> > Subsequently a write message could end up in the wrong register. This
> > could cause unpredictable system behavior.
> >
> > The DA9063 PMIC also supports an I2C compliant mode for the 2-wire
> > interface. This mode does not reset the interface when the clock
> > signal ceases. Thus the problem depicted above does not occur.
> >
> > This patch makes the I2C mode configurable by device tree. The SMBus
> > compliant mode is kept as the default.
>=20
> Could we not just check the bus' functionality flags and set this accordi=
ngly?
> Something like this is already done in regmap-i2c to determine how to acc=
ess
> the device:
>=20
>  https://elixir.bootlin.com/linux/latest/source/drivers/base/regmap/regma=
p-i2c.c#L309
>=20
> This seems cleaner than a new DT property, or will this not work in this
> situation?

Thank you for the proposal. We were not aware of this possibility.

We experienced the SMBus timeout problem on a i.MX6 Solo. When looking
at the i2c-imx driver we see that it defines a list of functionality.

	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL
		| I2C_FUNC_SMBUS_READ_BLOCK_DATA;

https://elixir.bootlin.com/linux/latest/source/drivers/i2c/busses/i2c-imx.c=
#L1133

None of that seems to model the inability to perform atomic transactions
within the SMBus timeout. This is either a bug of this specific driver
or maybe the expressiveness of I2C_FUNC_* is not sufficient.

https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/i2c.h#L88

What flag do you think we could check to find out whether the bus is
able to obey the SMBus timeout or not?

> > Signed-off-by: Hubert Streidl <hubert.streidl@de.bosch.com>
> > Signed-off-by: Mark Jonas <mark.jonas@de.bosch.com>
> > ---
> >  Documentation/devicetree/bindings/mfd/da9063.txt |  7 +++++++
> >  drivers/mfd/da9063-core.c                        |  9 +++++++++
> >  drivers/mfd/da9063-i2c.c                         | 13 +++++++++++++
> >  include/linux/mfd/da9063/core.h                  |  1 +
> >  include/linux/mfd/da9063/registers.h             |  3 +++
> >  5 files changed, 33 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/mfd/da9063.txt
> > b/Documentation/devicetree/bindings/mfd/da9063.txt
> > index 8da879935c59..256f2a25fe0a 100644
> > --- a/Documentation/devicetree/bindings/mfd/da9063.txt
> > +++ b/Documentation/devicetree/bindings/mfd/da9063.txt
> > @@ -19,6 +19,12 @@ Required properties:
> >  - interrupts : IRQ line information.
> >  - interrupt-controller
> >
> > +Optional properties:
> > +
> > +- i2c-mode : Switch serial 2-wire interface into I2C mode. Without
> > +this
> > +  property the PMIC uses the SMBus mode (resets the interface if the
> > +clock
> > +  ceases for a longer time than the SMBus timeout).
> > +
> >  Sub-nodes:
> >
> >  - regulators : This node defines the settings for the LDOs and BUCKs.
> > @@ -77,6 +83,7 @@ Example:
> >  		interrupt-parent =3D <&gpio6>;
> >  		interrupts =3D <11 IRQ_TYPE_LEVEL_LOW>;
> >  		interrupt-controller;
> > +		i2c-mode;
> >
> >  		rtc {
> >  			compatible =3D "dlg,da9063-rtc";
> > diff --git a/drivers/mfd/da9063-core.c b/drivers/mfd/da9063-core.c
> > index df407c3afce3..baa1e4310c8c 100644
> > --- a/drivers/mfd/da9063-core.c
> > +++ b/drivers/mfd/da9063-core.c
> > @@ -162,6 +162,15 @@ int da9063_device_init(struct da9063 *da9063,
> > unsigned int irq)  {
> >  	int ret;
> >
> > +	if (da9063->i2cmode) {
> > +		ret =3D regmap_update_bits(da9063->regmap,
> > DA9063_REG_CONFIG_J,
> > +				DA9063_TWOWIRE_TO, 0);
> > +		if (ret < 0) {
> > +			dev_err(da9063->dev, "Cannot enable I2C mode.\n");
> > +			return -EIO;
> > +		}
> > +	}
> > +
> >  	ret =3D da9063_clear_fault_log(da9063);
> >  	if (ret < 0)
> >  		dev_err(da9063->dev, "Cannot clear fault log\n"); diff --git
> > a/drivers/mfd/da9063-i2c.c b/drivers/mfd/da9063-i2c.c index
> > 3781d0bb7786..af0bf13ab43e 100644
> > --- a/drivers/mfd/da9063-i2c.c
> > +++ b/drivers/mfd/da9063-i2c.c
> > @@ -351,6 +351,17 @@ static const struct of_device_id da9063_dt_ids[] =
=3D {
> >  	{ }
> >  };
> >  MODULE_DEVICE_TABLE(of, da9063_dt_ids);
> > +
> > +static void da9063_i2c_parse_dt(struct i2c_client *client, struct
> > +da9063 *da9063) {
> > +	struct device_node *np =3D client->dev.of_node;
> > +
> > +	if (of_property_read_bool(np, "i2c-mode"))
> > +		da9063->i2cmode =3D true;
> > +	else
> > +		da9063->i2cmode =3D false;
> > +}
> > +
> >  static int da9063_i2c_probe(struct i2c_client *i2c,
> >  			    const struct i2c_device_id *id)  { @@ -366,6 +377,8
> @@ static
> > int da9063_i2c_probe(struct i2c_client *i2c,
> >  	da9063->chip_irq =3D i2c->irq;
> >  	da9063->type =3D id->driver_data;
> >
> > +	da9063_i2c_parse_dt(i2c, da9063);
> > +
> >  	ret =3D da9063_get_device_type(i2c, da9063);
> >  	if (ret)
> >  		return ret;
> > diff --git a/include/linux/mfd/da9063/core.h
> > b/include/linux/mfd/da9063/core.h index fa7a43f02f27..866864c50f78
> > 100644
> > --- a/include/linux/mfd/da9063/core.h
> > +++ b/include/linux/mfd/da9063/core.h
> > @@ -77,6 +77,7 @@ struct da9063 {
> >  	enum da9063_type type;
> >  	unsigned char	variant_code;
> >  	unsigned int	flags;
> > +	bool	i2cmode;
> >
> >  	/* Control interface */
> >  	struct regmap	*regmap;
> > diff --git a/include/linux/mfd/da9063/registers.h
> > b/include/linux/mfd/da9063/registers.h
> > index 1dbabf1b3cb8..6e0f66a2e727 100644
> > --- a/include/linux/mfd/da9063/registers.h
> > +++ b/include/linux/mfd/da9063/registers.h
> > @@ -1037,6 +1037,9 @@
> >  #define		DA9063_NONKEY_PIN_AUTODOWN	0x02
> >  #define		DA9063_NONKEY_PIN_AUTOFLPRT	0x03
> >
> > +/* DA9063_REG_CONFIG_J (addr=3D0x10F) */
> > +#define DA9063_TWOWIRE_TO			0x40
> > +
> >  /* DA9063_REG_MON_REG_5 (addr=3D0x116) */
> >  #define DA9063_MON_A8_IDX_MASK			0x07
> >  #define		DA9063_MON_A8_IDX_NONE		0x00
> > --
> > 2.25.1

Cheers,
Mark