linux-kernel - Re: [PATCH v3 1/4] i2c: mux-pinctrl: Rework to honor disabled child nodes

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Date:	Thu, 19 Mar 2015 17:02:08 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Gabriel Dobato <dobatog@...il.com>, linux-i2c@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] i2c: mux-pinctrl: Rework to honor disabled child
 nodes

> >-	/* Only register child devices if the adapter has a node pointer set */
> >-	if (!adap->dev.of_node)
> >+	/* Only register childs if adapter has a node pointer with enabled status */
> >+	if (!adap->dev.of_node || !of_device_is_available(adap->dev.of_node))
> >  		return;
> 
> That feels a bit odd to me. For a regular non-mux I2C controller, that extra
> case would never trigger if the controller node was disabled, since the
> device core would never probe the controller device itself. So, we'd end up
> with inconsistent paths through the I2C core for regular controllers and
> muxes.

I first thought the no-op for the non-mux case wouldn't hurt, but I
agree about the consistent code path. I mentioned in my previous mail
that i2c-mux might be a better place for this...

> Perhaps better would be to have a mux-specific function to iterate over a
> mux's child nodes and instantiate buses for those. That function would check
> whether each bus node was disabled or not. That'd isolate the special case
> into the place where it was relevant.

... so I wonder what you think about putting the
of_device_is_available() check into i2c_add_mux_adapter() once the
reg-property and chan_id have been matched?


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