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

From: Maxime Ripard
Date: Wed May 13 2015 - 13:55:11 EST

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 Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering

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