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

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Date:	Thu, 19 Feb 2015 10:57:56 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Pantelis Antoniou <panto@...oniou-consulting.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Matt Porter <matt.porter@...aro.org>,
	Koen Kooi <koen@...inion.thruhere.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

On Thu, Feb 19, 2015 at 10:36:00AM -0800, Tony Lindgren wrote:
> * 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 would not work for my use case. Again, this is a CPU card
plugged into a carrier card, of which there are several variants.
The CPU card is similar to a Com Express card (not exactly the same,
but the same idea), so it may even be manufactured by a third party.
Actually, in some cases it is. Modifying the kernel command line
based on the carrier card it is connected to is simply not possible.

Guenter
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