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Date:   Mon, 15 Mar 2021 19:31:15 +0100
From:   Wolfram Sang <wsa@kernel.org>
To:     Mark Jonas <mark.jonas@de.bosch.com>
Cc:     Support Opensource <support.opensource@diasemi.com>,
        Lee Jones <lee.jones@linaro.org>, linux-kernel@vger.kernel.org,
        linux-i2c@vger.kernel.org, Adam.Thomson.Opensource@diasemi.com,
        stwiss.opensource@diasemi.com, marek.vasut@gmail.com,
        tingquan.ruan@cn.bosch.com, hubert.streidl@de.bosch.com
Subject: Re: [PATCH v5] mfd: da9063: Support SMBus and I2C mode
Message-ID: <20210315183115.GA2343@kunai>
Mail-Followup-To: Wolfram Sang <wsa@kernel.org>,
        Mark Jonas <mark.jonas@de.bosch.com>,
        Support Opensource <support.opensource@diasemi.com>,
        Lee Jones <lee.jones@linaro.org>, linux-kernel@vger.kernel.org,
        linux-i2c@vger.kernel.org, Adam.Thomson.Opensource@diasemi.com,
        stwiss.opensource@diasemi.com, marek.vasut@gmail.com,
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References: <20210315160903.799426-1-mark.jonas@de.bosch.com>
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On Mon, Mar 15, 2021 at 05:09:03PM +0100, Mark Jonas wrote:
> From: Hubert Streidl <hubert.streidl@de.bosch.com>
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> This patch enables the I2C bus mode if I2C_FUNC_I2C is set or
> otherwise keeps the default SMBus mode.
>=20
> Signed-off-by: Hubert Streidl <hubert.streidl@de.bosch.com>
> Signed-off-by: Mark Jonas <mark.jonas@de.bosch.com>

=46rom an I2C point of view, this is the correct approach:

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>


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