linux-kernel - Re: [PATCH] spi: Force the registration of the spidev devices

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Date:	Wed, 13 May 2015 19:50:34 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
	Hans de Goede <hdegoede@...hat.com>,
	linux-spi@...r.kernel.org, Martin Sperl <kernel@...tin.sperl.org>,
	Michal Suchanek <hramrach@...il.com>
Subject: Re: [PATCH] spi: Force the registration of the spidev devices

Hi Greg,

On Wed, May 13, 2015 at 08:37:40AM -0700, Greg Kroah-Hartman wrote:
> On Wed, May 13, 2015 at 12:26:04PM +0100, Mark Brown wrote:
> > On Tue, May 12, 2015 at 10:33:24PM +0200, Maxime Ripard wrote:
> > 
> > > While this is nicer than the DT solution because of its accurate hardware
> > > representation, it's still not perfect because you might not have access to the
> > > DT, or you might be driving a completely generic device (such as a
> > > microcontroller) that might be used for something else in a different
> > > context/board.
> > 
> > Greg, you're copied on this because this seems to be a generic problem
> > that should perhaps be solved at a driver model level - having a way to
> > bind userspace access to devices that we don't otherwise have a driver
> > for.  The subsystem could specify the UIO driver to use when no other
> > driver is available.
> 
> That doesn't really work.  I've been talking to the ACPI people about
> this, and the problem is "don't otherwise have a driver for" is an
> impossible thing to prove, as you never know when a driver is going to
> be loaded from userspace.
> 
> You can easily bind drivers to devices today from userspace, why not
> just use the built-in functionality you have today if you "know" that
> there is no driver for this hardware.

What we're really after here is that we want to have an spidev
instance when we don't even have a device.

And since SPI isn't really doing any kind of hotplug, the only
situation that might be problematic is if we have the DT overlays
registering new devices.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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