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

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Date:	Thu, 19 Feb 2015 20:44:39 +0200
From:	Pantelis Antoniou <panto@...oniou-consulting.com>
To:	Tony Lindgren <tony@...mide.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

Hi Tony,

> On Feb 19, 2015, at 20:36 , Tony Lindgren <tony@...mide.com> 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..
> 

The way it’s done right now is with minimal code. Reading the EEPROM
is required.

>> 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.
> 

You assume there’s going to be a bootloader…

> Regards,
> 
> Tony

Regards

— Pantelis

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