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

[Eddie James]

On 5/12/22 11:48, Jonathan Cameron wrote:
> On Thu, 12 May 2022 11:20:18 -0500
> Eddie James <eajames@xxxxxxxxxxxxx> 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.


Agreed, but locking the bus doesn't work in the case where the chip is 
behind a mux. The mux core driver deselects the mux immediately after 
the transfer to reset the si7020, causing some i2c traffic, breaking the 
si7020. So it would also be a requirement to configure the mux to idle 
as-is... That's why I went with the optional skipping of the reset. 
Maybe I should add the bus lock too?


Thanks,

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