linux-kernel - Re: [PATCH 7/7] OF/ACPI/I2C: Add generic match function for the aforementioned systems

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Message-Id: <20140606234253.A4E25C427F0@trevor.secretlab.ca>
Date:	Sat, 07 Jun 2014 00:42:53 +0100
From:	Grant Likely <grant.likely@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>, Mark Brown <broonie@...nel.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Linux I2C <linux-i2c@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 7/7] OF/ACPI/I2C: Add generic match function for the
 aforementioned systems

On Fri, 6 Jun 2014 13:36:53 +0100, Lee Jones <lee.jones@...aro.org> wrote:
> On Fri, 06 Jun 2014, Mark Brown wrote:
> 
> > On Thu, Jun 05, 2014 at 04:55:09PM +0100, Lee Jones wrote:
> > > On Thu, 05 Jun 2014, Grant Likely wrote:
> > 
> > > > I still think the way to do it is to emulate the missing i2c_device_id
> > > > when calling the drivers .probe() hook by having a temporary copy on
> > > > the stack and filling it with data from the OF or ACPI table....
> > 
> > > That's the opposite of what I'm trying to achieve.  I'm trying to get
> > > rid of unused i2c_device_id tables, rather than reinforce their
> > > mandatory existence.  I think an i2c_of_match_device() with knowledge
> > > of how to match via pure DT principles (of_node/compatible) and a
> > > fall-back, which is able to match on a provided of_device_id table
> > > alone i.e. without the requirement of an existing of_node.
> > 
> > > I've also been mulling over the idea of removing the second probe()
> > > parameter, as suggested by Wolfram.  However, this has quite deep
> > > ramifications which would require a great deal of driver adaptions.
> > 
> > If you're going to do that another option is to refactor the probe()
> > function to take the driver_data as an argument and then have the core
> > pass that from whatever table it matched from rather than the entire
> > i2c_device_id structure.  That way the driver just needs to supply all
> > the ID tables mapping binding information to whatever it needs and the
> > core can pass in the driver data from whatever table it matched against.
> 
> Unfortunately this means we're back to the aforementioned typing
> issue.  For struct {platform,i2c,spi,acpi,etc}_device_id the driver
> data is a kernel ulong but the of_device_id's driver data attribute is
> a void*.

We're actually okay there. Each subsystem defines it's own convention
about what those values mean. ulong and void* are the same size and
every user I've seen stuffs the same data into the data field of both
tables.

> I've just started work on a migration over to a new probe().  I don't
> think it's all that much work, but if there are any objections I'd
> prefer to hear them now rather than waste any time.

I have no problem with that approach.

> I propose to convert a couple of drivers, one which doesn't use the
> driver_data and one that does, but is DT only and send them for
> review.  See if Wolfram et. al like the method.
> 
> -- 
> Lee Jones
> Linaro STMicroelectronics Landing Team Lead
> Linaro.org │ Open source software for ARM SoCs
> Follow Linaro: Facebook | Twitter | Blog

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