linux-kernel - Re: [PATCH v2 0/2] iio: humidity: si7020: Check device property for skipping reset in probe

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Date:   Sat, 14 May 2022 14:40:30 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Eddie James <eajames@...ux.ibm.com>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, krzysztof.kozlowski+dt@...aro.org,
        robh+dt@...nel.org, lars@...afoo.de, miltonm@...ibm.com
Subject: Re: [PATCH v2 0/2] iio: humidity: si7020: Check device property for
 skipping reset in probe

On Thu, 12 May 2022 14:11:06 -0500
Eddie James <eajames@...ux.ibm.com> wrote:

> On 5/12/22 11:48, Jonathan Cameron wrote:
> > On Thu, 12 May 2022 11:20:18 -0500
> > Eddie James <eajames@...ux.ibm.com> wrote:
> >  
> >> I2C commands issued after the SI7020 is starting up or after reset
> >> can potentially upset the startup sequence. Therefore, the host
> >> needs to wait for the startup sequence to finish before issuing
> >> further i2c commands. This is impractical in cases where the SI7020
> >> is on a shared bus or behind a mux, which may switch channels at
> >> any time (generating I2C traffic). Therefore, check for a device
> >> property that indicates that the driver should skip resetting the
> >> device when probing.  
> > Why not lock the bus?  It's not ideal, but then not resetting and hence
> > potentially ending up in an unknown state isn't great either.  
> 
> 
> Also, I should mention that in our case we can rely on the power on 
> reset, so the device should be in a known state.

Until someone unbinds and rebinds the driver...
It's very hard to have any guarantees once users are involved :)

Jonathan


> 
> Eddie
> 
> 
> >
> > Jonathan
> >  
> >> Changes since v1:
> >>   - Fix dt binding document
> >>
> >> Eddie James (2):
> >>    dt-bindings: iio: humidity: Add si7020 bindings
> >>    iio: humidity: si7020: Check device property for skipping reset in probe
> >>
> >>   .../bindings/iio/humidity/silabs,si7020.yaml  | 47 +++++++++++++++++++
> >>   .../devicetree/bindings/trivial-devices.yaml  |  2 -
> >>   drivers/iio/humidity/si7020.c                 | 14 +++---
> >>   3 files changed, 55 insertions(+), 8 deletions(-)
> >>   create mode 100644 Documentation/devicetree/bindings/iio/humidity/silabs,si7020.yaml
> >>