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

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Message-ID: <54EB73DC.4090507@hurleysoftware.com>
Date:	Mon, 23 Feb 2015 13:39:24 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Pantelis Antoniou <panto@...oniou-consulting.com>,
	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 Pantelis,

On 02/19/2015 01:44 PM, Pantelis Antoniou wrote:
> 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…

So does this patch.

> diff --git a/arch/arm/mach-omap2/am33xx-dt-quirks.c b/arch/arm/mach-omap2/am33xx-dt-quirks.c
[...]
> + * Note that we rely on the bootloader setting up the muxes
> + * (which is the case for u-boot).

Regards,
Peter Hurley

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