linux-kernel - Re: [PATCH 3/4] arm: am33xx: DT quirks for am33xx based beaglebone variants

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Message-ID: <20150219183600.GG32521@atomide.com>
Date:	Thu, 19 Feb 2015 10:36:00 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Pantelis Antoniou <panto@...oniou-consulting.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Matt Porter <matt.porter@...aro.org>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	Rob Herring <robherring2@...il.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	devicetree@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] arm: am33xx: DT quirks for am33xx based beaglebone
 variants

* Pantelis Antoniou <panto@...oniou-consulting.com> [150219 10:32]:
> > On Feb 19, 2015, at 20:16 , Tony Lindgren <tony@...mide.com> wrote:
> > 
> > Uhh I don't like the idea of duplicating the i2c-omap.c driver under
> > arch/arm.. And in general we should initialize things later rather
> > than earlier.
> > 
> > What's stopping doing these quirk checks later on time with just
> > a regular device driver, something like drivers/misc/bbone-quirks.c?
> > 
> 
> We have no choice; we are way early in the boot process, right after
> the device tree unflattening step.

To me it seems the dt patching part should be done with minimal
code before any driver like features..
 
> I’ve toyed with the idea of using early platform devices but the omap-i2c driver
> would need some tender love and care to make it work, and I didn’t want to get
> bogged down with i2c driver details at this point.

..so how about just parse a kernel cmdline for the quirks to apply
based on a version string or similar? That can be easily populated
by u-boot or set manually with setenv.

That leaves out the need for tinkering with i2c super early in
the kernel for revision detection.

Regards,

Tony
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