linux-kernel - RE: [PATCH v2] mfd: da9063: Support SMBus and I2C mode

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Date:   Thu, 4 Feb 2021 16:09:28 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Mark Jonas <mark.jonas@...bosch.com>,
        Support Opensource <Support.Opensource@...semi.com>,
        Lee Jones <lee.jones@...aro.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Steve Twiss <stwiss.opensource@...semi.com>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "tingquan.ruan@...bosch.com" <tingquan.ruan@...bosch.com>,
        "hubert.streidl@...bosch.com" <hubert.streidl@...bosch.com>,
        Wolfram Sang <wsa@...nel.org>
Subject: RE: [PATCH v2] mfd: da9063: Support SMBus and I2C mode

On 04 February 2021 15:52, Mark Jonas wrote:

> From: Hubert Streidl <hubert.streidl@...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 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 tests for the bus functionality "I2C_FUNC_I2C". It can
> reasonably be assumed that the bus cannot obey SMBus timings if
> this functionality is set. SMBus commands most probably are emulated
> in this case which is prone to the latency issue described above.
> 
> This patch enables the I2C bus mode if I2C_FUNC_I2C is set or
> otherwise enables the SMBus mode for a native SMBus controller
> which doesn't have I2C_FUNC_I2C set.
> 
> Signed-off-by: Hubert Streidl <hubert.streidl@...bosch.com>
> Signed-off-by: Mark Jonas <mark.jonas@...bosch.com>
> ---
> Changes in v2:
>   - Implement proposal by Adam Thomson and Wolfram Sang to check for
>     functionality I2C_FUNC_I2C instead of introducing a new DT property.
> 
>  drivers/mfd/da9063-i2c.c             | 15 +++++++++++++++
>  include/linux/mfd/da9063/registers.h |  3 +++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/mfd/da9063-i2c.c b/drivers/mfd/da9063-i2c.c
> index 3781d0bb7786..a2245253f039 100644
> --- a/drivers/mfd/da9063-i2c.c
> +++ b/drivers/mfd/da9063-i2c.c
> @@ -355,6 +355,7 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
>  			    const struct i2c_device_id *id)
>  {
>  	struct da9063 *da9063;
> +	unsigned int busmode;
>  	int ret;
> 
>  	da9063 = devm_kzalloc(&i2c->dev, sizeof(struct da9063), GFP_KERNEL);
> @@ -442,6 +443,20 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
>  		return ret;
>  	}
> 
> +	if (i2c_check_functionality(i2c->adapter, I2C_FUNC_I2C)) {
> +		dev_info(da9063->dev, "I2C mode");
> +		busmode = 0;
> +	} else {
> +		dev_info(da9063->dev, "SMBus mode");
> +		busmode = 1;

I think this should be 'DA9063_TWOWIRE_TO' rather than '1' otherwise I think
you'll be setting 0 still here as it doesn't match up with the mask.

> +	}
> +	ret = regmap_update_bits(da9063->regmap, DA9063_REG_CONFIG_J,
> +		DA9063_TWOWIRE_TO, busmode);
> +	if (ret < 0) {
> +		dev_err(da9063->dev, "Failed to set 2-wire bus mode.\n");
> +		return -EIO;
> +	}
> +
>  	return da9063_device_init(da9063, i2c->irq);
>  }
> 
> 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=0x10F) */
> +#define DA9063_TWOWIRE_TO			0x40
> +
>  /* DA9063_REG_MON_REG_5 (addr=0x116) */
>  #define DA9063_MON_A8_IDX_MASK			0x07
>  #define		DA9063_MON_A8_IDX_NONE		0x00
> --
> 2.25.1