[U-Boot] Help with exporting memory power management info in u-boot

[Ankita Garg]

Hi,

On Mon, May 30, 2011 at 11:49:26AM +0200, Wolfgang Denk wrote:
> Dear Ankita Garg,
> 
> In message <20110530063940.GB16331 at in.ibm.com> you wrote:
> > 
> > In this regard, we want some help from the u-boot community on designing
> > the interfaces. Further, we would like to collaborate with all the SoCs
> > that have support for managing memory power on their boards, so we could
> > design a generic interface that can be exploited by all.
> 
> Could you please be so kind and explain which of such functionality
> you envision to see in ore expect from U-Boot?
> 
> I understand why all thisi s a very important topic for an operating
> system like Linux.
> 
> But U-Boot is a boot loader.  It is being used mainly in two different
> environments or usage modes:
> 
> 1) First, U-Boot is a powerful tool for board bringup and for software
>    development purposes.  In this environment, power consumption is
>    usually the least of your concerns.  Instead, we focus on
>    simplicity and robustness.
> 
> 2) Second, U-Boot is (sometimes) an inevitable intermediate step when
>    booting an operating system.  In this mode, whole purpose of U-Boot
>    is to get it's job done and then get out of the way as quickly as
>    possible.
> 
> So in real-world applications we may see a few ten, or maybe in worst
> case up to a few hundred milliseconds of U-Boot runtime compared to
> hours, days and often weeks and months of run time of the respective
> operating system.
> 
> 
> Keeping this in mind, which are the parts of memory power management
> that are important for the U-Boot context?
>

I agree with the above. Its not the power consumed by u-boot that is of
concern. We want u-boot support in exporting additional information to
the kernel, regarding the memory hardware characteristics specific to
power management. For instance, if u-boot could inform the kernel about
the boundaries at which PASR is supported on the underlying platform,
that information could then be used by the kernel to exploit this
feature. Like, this information would be encapsulated in a device-tree
node maybe ?
 
-- 
Regards,
Ankita Garg (ankita at in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India