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

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

[Ankita Garg]

Hi,

Memory hardware today offers capabilities for managing power
consumption, like multiple lower power statest. Few SoCs, like the TI
Panda board, offers support for Partial Array Self Refresh (PASR), by
which partial areas of memory could be turned off to save power.
Further, few other SoCs have multiple memory controllers, like Samsung
Exynos 4210, where each controller independently transitions memory
under it into lower power states depending on certain criteria. Each of
these capabilities are supported by the hardware at a particular
granularity. For example, PASR could be supported at the level of a
memory bank, i.e, a bank of memory that is free could be turned off,
independent of the other banks.

Inorder to exploit these features, the Linux VM subsystem needs to be
modified to take into account the physical memory topology when managing
memory. We proposed a generic memory regions infrastructure, that could
be used to tag boundaries of memory blocks which belong to a specific
memory power management domain and further enable exploitation of
platform capabilities. The details of this framework can be found here:

https://lkml.org/lkml/2011/5/27/177

Memory region is a layer of abstraction that would be created at boot
time, with information from firmware regarding the granularity at which
memory power can be managed on the platform. We would like to work
towards having this information exported by u-boot. A sample interface
we are looking at is a device tree node that would provide the number,
size and starting address corresponding to the memory power domains on
the underlying platform.

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.

-- 
Regards,
Ankita Garg (ankita at in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India

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

[Wolfgang Denk]

Dear Ankita Garg,

In message <20110530063940.GB16331@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?

Thanks.


Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
It's not an optical illusion, it just looks like one.   -- Phil White

[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@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

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

[Wolfgang Denk]

Dear Ankita Garg,

In message <20110530102030.GD18375@in.ibm.com> you wrote:
> 
> 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 ?

I agree that is is a good idea to encode such information in the
device tree.  U-Boot can also help to update memory related notes in
the device tree, for example by inserting their actual physical
addresses and sizes.

The rest, including information about memory power management
properties of such nodes in the device tree, is of no concern to
U-Boot and should just be passed on unchanged.

In my opinion it is therefore the responsibility of the creator of
the device tree to provide a proper description of the hardware,
including the memory power management information.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Democracy is mob rule, but with income taxes.

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

[Ankita Garg]

Hi,

On Mon, May 30, 2011 at 01:01:57PM +0200, Wolfgang Denk wrote:
> Dear Ankita Garg,
> 
> In message <20110530102030.GD18375@in.ibm.com> you wrote:
> > 
> > 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 ?
> 
> I agree that is is a good idea to encode such information in the
> device tree.  U-Boot can also help to update memory related notes in
> the device tree, for example by inserting their actual physical
> addresses and sizes.
> 
> The rest, including information about memory power management
> properties of such nodes in the device tree, is of no concern to
> U-Boot and should just be passed on unchanged.
> 
> In my opinion it is therefore the responsibility of the creator of
> the device tree to provide a proper description of the hardware,
> including the memory power management information.
>

Ok, thats true. So I guess a better place would be the linux-arm-kernel
list to discuss about potential device-tree interface design.
Thanks Wolfgang !
 
-- 
Regards,
Ankita Garg (ankita at in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India

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

[Wolfgang Denk]

Dear Ankita Garg,

In message <20110530170917.GC23950@in.ibm.com> you wrote:
>
> > In my opinion it is therefore the responsibility of the creator of
> > the device tree to provide a proper description of the hardware,
> > including the memory power management information.
> 
> Ok, thats true. So I guess a better place would be the linux-arm-kernel
> list to discuss about potential device-tree interface design.

Indeed.

> Thanks Wolfgang !

You are welcome.  Please feel free to keep the U-Boot list on Cc: with
any topics where the boot loader might help to fill in any parameters
that should better be determined dynalically.  We'll be happy to help
with that.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"I didn't know it was impossible when I did it."