linux-kernel - Re: [PATCH v4 3/3] iio: light: Add support for ltrf216a sensor

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Date:   Fri, 13 May 2022 20:59:29 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Shreeya Patel <shreeya.patel@...labora.com>, jic23@...nel.org,
        lars@...afoo.de, robh+dt@...nel.org, Zhigang.Shi@...eon.com,
        krisman@...labora.com
Cc:     linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...labora.com,
        alvaro.soliverez@...labora.com
Subject: Re: [PATCH v4 3/3] iio: light: Add support for ltrf216a sensor

13.05.2022 16:40, Shreeya Patel пишет:
> Also, why would we want to do a SW reset here?
> 
> In the datasheet, I could see the following steps to enable the sensor
> Supply VDD to Sensor (Sensor in Standby Mode) ---> Wait 100 ms (min) -
> initial startup time
> ---> I2C Command (Write) To enable sensor to Active Mode

For example, if you'll do kexec from other kernel, say downstream
kernel, then the h/w state is undetermined for us. It's a common problem
with downstream drivers that they rely on a specific state left from
bootloader, which is often unacceptable for upstream.

If we'll do the SW reset on probe, then we'll bring h/w into the
predictable state and won't depend on state left from bootloader or
anything else that touched h/w before us.