[U-Boot] [PATCH 09/14] tegra: Add warmboot implementation

[Stephen Warren]

On 01/13/2012 04:05 PM, Simon Glass wrote:
> On Fri, Jan 13, 2012 at 2:04 PM, Yen Lin <yelin at nvidia.com> wrote:
>> On Fri, 2012-01-13 at 11:34 -0800, Simon Glass wrote:
>>> On Tue, Jan 10, 2012 at 10:30 AM, Stephen Warren <swarren at nvidia.com> wrote:
>>>> On 12/26/2011 12:33 PM, Simon Glass wrote:
...
>>> But there a few questions here. Firstly it seems that it saves some
>>> memory speed info to scratch2 but never restores it. Then it restores
>>> CPU speed from scratch3 but I can't see where it saves it. Does Yen
>>> have any comments on that? Apparently it works because we have been
>>> using it, but... If it is saving things that are never restored I
>>> could dump that and reduce the code size.
>>>
>>
>> U-boot code saves sdram parameters to scratch2, scratch4, and scratch 24
>> registers, so when system resumes, bootrom can restore sdram parameters
>> from these registers.
>>
>> The scratch3 register content was saved by kernel before suspend, and is
>> used by the warmboot code to restore PLLX settings.
> 
> Thanks for the info.
> 
> On resume I do not see it using scratch2, 4 or 24 within U-Boot. Are
> those used in the kernel?

The Tegra boot ROM (which contains the power-on code for the AVP) is
what interprets these, according to Yen above.

One question for Yen: Why doesn't the boot ROM read the SDRAM parameters
from the BCT like it does during a cold boot? Perhaps there's some
interaction with clock settings, so the boot ROM needs to know the
clock/voltage/... state the kernel was in when suspending, rather than
just using the "usual" cold boot settings?

> I should add something to document this so the kernel people can match
> up when that side of it goes up stream.

-- 
nvpublic