linux-kernel - Re: [RFC 0/4] Add support for the Gateworks System Controller

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Date:   Wed, 28 Feb 2018 17:56:18 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     Lee Jones <lee.jones@...aro.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-input@...r.kernel.org
Subject: Re: [RFC 0/4] Add support for the Gateworks System Controller

Hi Tim

Cool. I would say this is done right.

> One issue I'm trying to figure out the best way to deal with is the
> fact that the GSC can 'NAK' transactions occasionally which is why I
> override the regmap read/write functions and provide retries. This
> resolves the issue for the mfd core driver and sub-module drivers but
> doesn't resolve the issue with these 'emulated devices' which have
> their own stand-alone drivers. I'm not sure how to best deal with that
> yet. I tried to add retires to the i2c adapter but that wasn't
> accepted upstream because it was too generic and I was told I need to
> work around it in device-drivers.

How about writing an i2c bus driver which sits directly on top of
another i2c bus? Basically a one port i2c mux.

The current mux code does not seem to directly allow it, since it
calls i2c_transfer() directly on the parent, where as you want it to
call your own i2c_transfer function. But maybe you could expended the
core mux code to allow the i2c_mux_core structure to contain a transfer
function?

      Andrew