From: Igor Grinberg <grinberg@compulab.co.il>
To: Stephen Warren <swarren@wwwdotorg.org>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>,
Wolfgang Denk <wd@denx.de>, Arnd Bergmann <arnd@arndb.de>,
linux-arm-kernel@lists.infradead.org,
Lee Jones <lee.jones@linaro.org>,
Samuel Ortiz <sameo@linux.intel.com>,
Arnd Bergmann <arnd@ardb.de>, Olof Johansson <olof@lixom.net>,
linux-embedded@vger.kernel.org, linux-kernel@vger.kernel.org,
Linus Walleij <linus.walleij@linaro.org>
Subject: Re: Handling of modular boards
Date: Fri, 11 May 2012 09:15:04 +0300 [thread overview]
Message-ID: <4FACAE68.2090004@compulab.co.il> (raw)
In-Reply-To: <4FABE9BE.2010108@wwwdotorg.org>
On 05/10/12 19:15, Stephen Warren wrote:
> On 05/10/2012 06:40 AM, Igor Grinberg wrote:
>> On 05/05/12 01:09, Mark Brown wrote:
>>> On Fri, May 04, 2012 at 10:33:57PM +0200, Wolfgang Denk wrote:
>>
>>>> On the other hand, some of the issues we're trying to solve
>>>> here for the kernel are also present in the boot loader, so
>>>> this needs to do this anyway - whether by inserting new or
>>>> modifying (enabling or disabling) existing properties in the DT
>>>> is not really relevant here.
>>
>>> FWIW if the bootloader can usefully handle this stuff I think
>>> that's a good approach but there is substantial variation in
>>> quality of implementation between bootloaders and even when the
>>> bootloader is a good one it's not always practical to update it
>>> or the data it relies on.
>>
>> I agree on this (and also with Ben), all our boards/extensions/base
>> boards/etc can be discovered in the boot loader and we will use the
>> DT to pass the relevant information on the attached extensions and
>> used base board.
>>
>> Also, most (if not all) of our boards/extensions have I2C EEPROM
>> which describes the devices on that board/extension which is useful
>> for building/extending the DT in the bootloader.
>
> I believe that's true for all/many NVIDIA boards too.
>
> But, duplicating all this in every bootloader might not make sense.
Yeah, I agree on this, especially when you have multiple bootloaders
for the same board...
On the other hand, that is a common problem of the open source
software - anyone can create a bootloader, publish and use it...
> Sure there are some cases where the bootloader needs this information
> (e.g. to load the kernel from an SD card that's on 1 of N plugin
> boards), but there may be much information the bootloader doesn't care
> about.
>
> Would it make sense to write a DT-identifying-and-merging shim that
> can be executed by the bootloader, create the final DT, and then jump
> to the kernel?
>
> Hmmm. That's probably a bad idea, since then it means needing e.g. I2C
> drivers to read the ID EEPROMs, pinmux drivers, ... in the shim.
>
> Perhaps the common shim idea makes sense, but we need a standardized
> API it can use that all bootloaders provide for it to operate.
Let's see where we're heading:
We created/extended the DT to abstract all the SoC/board specific
(probably also undetectable) stuff away from the kernel and now we will
create a special shi(t)m that will interface the bootloader and create the DT?
I don't think it is a good idea, especially because you still need to change
the bootloader(s) and if you place the I2C/pinmux/gpio drivers inside that
shi(t)m, you duplicate the bootloader, no?
I think we should let the bootloader(s) create/extend the DT and if for some
reason a bootloader wants to separate the DT code into a shim, let it be so.
>
> This is beginning to sound a lot like a UEFI byte code module (I
> assume; I know little about them)
That's another curse... probably we will not get away from it...
--
Regards,
Igor.
next prev parent reply other threads:[~2012-05-11 6:15 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-04 18:58 Handling of modular boards Mark Brown
2012-05-04 19:34 ` Arnd Bergmann
2012-05-04 20:07 ` Mark Brown
2012-05-04 20:33 ` Wolfgang Denk
2012-05-04 20:39 ` Arnd Bergmann
2012-05-04 20:54 ` Wolfgang Denk
2012-05-04 21:03 ` Arnd Bergmann
2012-05-04 21:09 ` Stephen Warren
2012-05-04 21:52 ` Mark Brown
2012-05-04 22:09 ` Mark Brown
2012-05-10 10:41 ` Ben Dooks
2012-05-10 12:40 ` Igor Grinberg
2012-05-10 16:15 ` Stephen Warren
2012-05-11 6:15 ` Igor Grinberg [this message]
2012-05-08 12:26 ` Linus Walleij
2012-05-09 17:12 ` Mark Brown
2012-05-04 19:50 ` Stephen Warren
2012-05-04 20:38 ` Wolfgang Denk
2012-05-04 20:59 ` Stephen Warren
2012-05-04 20:44 ` Mark Brown
2012-05-08 12:33 ` Linus Walleij
2012-05-09 8:41 ` Alessandro Rubini
2012-05-10 10:43 ` Ben Dooks
2012-05-10 16:11 ` Stephen Warren
2012-05-04 22:55 ` Russell King - ARM Linux
2012-05-04 23:40 ` Mark Brown
2012-05-04 23:52 ` Russell King - ARM Linux
2012-05-05 0:03 ` Mark Brown
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