linux-kernel - Re: [PATCH 3/3] i2c: nomadik: Add Device Tree support to the Nomadik I2C driver

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Date:	Mon, 3 Sep 2012 15:19:13 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Rob Herring <rob.herring@...xeda.com>,
	devicetree-discuss@...ts.ozlabs.org,
	Stephen Warren <swarren@...dia.com>,
	Wolfram Sang <w.sang@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	STEricsson_nomadik_linux@...t.st.com, linus.walleij@...ricsson.com,
	arnd@...db.de, linux-i2c@...r.kernel.org
Subject: Re: [PATCH 3/3] i2c: nomadik: Add Device Tree support to the Nomadik
 I2C driver

On Mon, Sep 3, 2012 at 2:34 PM, Lee Jones <lee.jones@...aro.org> wrote:

> When booting DT booting take a different path and no platform data
> is passed. We can't boot DT AND register devices with platform data
> or else we will double probe every device. The only way to pass
> pdata when booting with DT is with AUX_DATA() and that's a hack to
> get around things we don't have support for yet. Up until now that
> has been DMA bindings, clock and pinctrl names and call-backs.

So if we pass some augmented platform data using AUX_DATA()
that appears as pdata in this case, and gets discarded.

Thus we cannot use AUX_DATA() to override a broken, as in
"the interrupt number is wrong" device tree.

> If DT is corrupt or missing the kernel will boot using platform
> data, but np will always be NULL, so we don't have the problem you
> were alluding to above.

That was not the problem I had in mind.

I had a valid, but incorrect device tree in mind. I.e the device
is there, but with wrong base address, or wrong IRQ number.

If pdata takes precedence, we can use AUX_DATA() to
override such errors from the platform, since drivers/of/platform.c
helpfully pokes in the auxdata as the platform data.
I thought this was one of the reasons why auxdata exist
at all.

Or is the proper solution to runtime-patch the device tree
per se in such cases? How is that actually done then?

Yours,
Linus Walleij
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