linux-kernel - RE: [PATCH v4] mfd: da9063: Support SMBus and I2C mode

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Message-ID: <PR3PR10MB41422B90076115ACCE07D2A5808E9@PR3PR10MB4142.EURPRD10.PROD.OUTLOOK.COM>
Date:   Tue, 9 Feb 2021 13:18:21 +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>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...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 v4] mfd: da9063: Support SMBus and I2C mode

On 08 February 2021 15:28, 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>

Thanks for your efforts. Looks sensible to me, so:

Reviewed-by: Adam Thomson <Adam.Thomson.Opensource@...semi.com>