linux-kernel - Re: [PATCH v5] mfd: da9063: Support SMBus and I2C mode

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Date:   Tue, 16 Mar 2021 07:21:43 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Mark Jonas <mark.jonas@...bosch.com>
Cc:     Support Opensource <support.opensource@...semi.com>,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Adam.Thomson.Opensource@...semi.com, stwiss.opensource@...semi.com,
        marek.vasut@...il.com, tingquan.ruan@...bosch.com,
        hubert.streidl@...bosch.com, Wolfram Sang <wsa@...nel.org>
Subject: Re: [PATCH v5] mfd: da9063: Support SMBus and I2C mode

On Mon, 15 Mar 2021, 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 keeps the default SMBus mode.
> 
> Signed-off-by: Hubert Streidl <hubert.streidl@...bosch.com>
> Signed-off-by: Mark Jonas <mark.jonas@...bosch.com>
> ---
>  drivers/mfd/da9063-i2c.c             | 10 ++++++++++
>  include/linux/mfd/da9063/registers.h |  3 +++
>  2 files changed, 13 insertions(+)

Code looks good to me now, thanks.

However, this doesn't look like it would pass checkpatch.

Have you tried to build with W=1 and checkpatch?

> diff --git a/drivers/mfd/da9063-i2c.c b/drivers/mfd/da9063-i2c.c
> index 3781d0bb7786..e8a022e697c5 100644
> --- a/drivers/mfd/da9063-i2c.c
> +++ b/drivers/mfd/da9063-i2c.c
> @@ -442,6 +442,16 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
>  		return ret;
>  	}
>  
> +	/* If SMBus is not available and only I2C is possible, enter I2C mode */
> +	if (i2c_check_functionality(i2c->adapter, I2C_FUNC_I2C)) {
> +		ret = regmap_clear_bits(da9063->regmap, DA9063_REG_CONFIG_J,
> +			  DA9063_TWOWIRE_TO);
> +		if (ret < 0) {
> +			dev_err(da9063->dev, "Failed to set Two-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

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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