On 01/13/2012 04:05 PM, Simon Glass wrote:
On Fri, Jan 13, 2012 at 2:04 PM, Yen Lin yelin@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@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.