linux-kernel - Re: [RFC] i2c: designware: Avoid initcall and initialize the driver like a regular one

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Message-ID: <20141222190233.GA1014@katana>
Date:	Mon, 22 Dec 2014 20:02:33 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Walter Lozano <walter@...guardiasur.com.ar>
Cc:	mika.westerberg@...ux.intel.com, Romain.Baeriswyl@...lis.com,
	atull@...nsource.altera.com, raymond.tan@...el.com,
	carlpeng008@...il.com, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] i2c: designware: Avoid initcall and initialize the driver
 like a regular one

On Mon, Dec 22, 2014 at 03:15:49PM -0300, Walter Lozano wrote:
> Currently, the driver is relying on a subsys_initcall() to register
> the platform driver struct. This is typically done to allow early uses
> of the I2C bus (for instance, I2C regulators used from early machine code).
> 
> While this might work on some cases, it breaks on others. For instance,
> I2C devices with GPIO-wired interrupts will fail to request the
> interrupt because of this initcall usage.
> 
> This commits attempts to fix the above issue, by converting the I2C
> driver into a regular kernel platform driver. This guarantees it will
> probe after GPIOs drivers.
> 
> Platforms based on devicetree won't be affected by this change.

Huh, why is that?

> Legacy platforms, relying on the I2C being available early, might need
> to implement proper defered mechanisms to overcome potential problems.

NAK. We can't say "Let's cause a regression to force people to fix
things that used to work" IMO. You exactly pointed out the problem that using
subsys_initcall() creates.

What about fixing the drivers you use to support deferred probing when
acquitin the irq?

Regards,

   Wolfram

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