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

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Message-Id: <8252298C-4249-49F8-91CA-8398ADEB1348@antoniou-consulting.com>
Date:	Mon, 23 Feb 2015 20:48:39 +0200
From:	Pantelis Antoniou <panto@...oniou-consulting.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Tony Lindgren <tony@...mide.com>,
	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 Peter,

> On Feb 23, 2015, at 20:39 , Peter Hurley <peter@...leysoftware.com> wrote:
> 
> 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.
> 

Proof of concept, first iteration… The beaglebone is just the prototype stage.

>> 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
> 

Regards

— Pantelis

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