linux-kernel - Re: [PATCH v6 1/1] mfd: da9063: Support SMBus and I2C mode

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Date:   Tue, 16 Mar 2021 17:07:22 +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 v6 1/1] mfd: da9063: Support SMBus and I2C mode

On Tue, 16 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>
> ---
> Changes in v6:
>   - Fixed checkpatch check 'unaligned broken line'.
> 
> Changes in v5:
>   - Restructured according to feedback by Lee Jones.
> 
> Changes in v4:
>   - Remove logging of selected 2-wire bus mode.
> 
> Changes in v3:
>   - busmode now contains the correct bit DA9063_TWOWIRE_TO
> 
> 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             | 10 ++++++++++
>  include/linux/mfd/da9063/registers.h |  3 +++
>  2 files changed, 13 insertions(+)

Applied with Wolfram's RB, thanks.

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