linux-kernel - Re: [PATCH 1/2] Boottime: A tool for automatic measurement of kernel/bootloader boot time

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Date:	Thu, 15 Nov 2012 18:31:43 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Lee Jones <lee.jones@...aro.org>,
	Kyungmin Park <kmpark@...radead.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux@....linux.org.uk, linus.walleij@...ricsson.com,
	jonas.aberg@...ricsson.com, will.deacon@....com,
	Mian Yousaf Kaukab <mian.yousaf.kaukab@...ricsson.com>
Subject: Re: [PATCH 1/2] Boottime: A tool for automatic measurement of
 kernel/bootloader boot time

On Thu, Nov 15, 2012 at 1:25 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 15 November 2012, Lee Jones wrote:
>>
>> > > +/* for automatic boot timing testcases */
>> > > +#define ATAG_BOOTTIME  0x41000403
>> > Where can I refer this ATAG usage? can you point out the reference URL
>> > or patches?
>>
>> I assumed this would be in Mainline u-boot, but apparently not.
>> On closer inspection of the internal ST-Ericsson u-boot, this
>> functionality appears to be provided by patches which currently
>> exist as delta. So in essence, the bootloader you use will have
>> to be patched in a similar way for you to retrieve information
>> surrounding bootloader boot times.
>>
>> And there was me thinking it was magic. ;)
>>
>
> And since we're moving away from ATAG on ux500 towards DT, it won't
> even work in the future. How essential is this part for the operation
> of your code?

To be fun we need some mechanism to pass this info from the
boot loader to the kernel.

I think most bootloaders are already dynamically altering their
device trees to put in things like memory size etc so this would
probably be done the same way: a standard binding like for
everything else, then put the data in there.

I don't know if Lee has a modifiable U-boot to try out such
concepts on though?

Yours,
Linus Walleij
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