[U-Boot] Statically allocate a range of physical memory to an OS image.

[U-Boot] Statically allocate a range of physical memory to an OS image.

[mazen.e]

Hello,

I want to execute a an OS (either Linux or Android) on the Arndale exynos
5250 board. The board features 2 GB of RAM. However, I want to statically
alloacate a specifc region of RAM (e.g. 1 GB) to be used by the OS,  While
the other 1 GB is reserved for other purposes.

 What is the best way to achieve this goal? do I need to change the FDT to
reflect only the region of memory that I want to be visible by the OS? or
can it be done througth the bootargs passed from uboot to the kernel?

 
Please share your ideas.

Many thanks.



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[U-Boot] Statically allocate a range of physical memory to an OS image.

[Wolfgang Denk]

Dear "mazen.e",

In message <1401177091915-180825.post@n7.nabble.com> you wrote:
> 
> I want to execute a an OS (either Linux or Android) on the Arndale exynos
> 5250 board. The board features 2 GB of RAM. However, I want to statically
> alloacate a specifc region of RAM (e.g. 1 GB) to be used by the OS,  While
> the other 1 GB is reserved for other purposes.

If you boot an OS, you don;t reserve any memory in U-Boot at all.  At
the moment U-Boot branches to the OS entry point, U-Boot is dead and
gone, including any memory alocation information that might have been
present in U-Boot.

It is then up to the OS to set up it's own memory manegement.

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
Every solution breeds new problems.

[U-Boot] Statically allocate a range of physical memory to an OS image.

[mazen.e]

Great, many thanks for this information.

On the other hand,  according to my basic understanding (Please correct me
if I am wrong), U-boot can pass through the bootargs env variable
information about available memory in the platform. For instance,  bootargs 
mem=512M at 0xA0000000 .. instructs the kernel that the available memory is 512
MB starting @ 0xA0000000, in such case the rest of the platform memory is
not even visible to the kernel and its MMU. Is this conclusion true?

Thank you very much.





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[U-Boot] Statically allocate a range of physical memory to an OS image.

[Wolfgang Denk]

Dear "mazen.e",

In message <1401191218533-180832.post@n7.nabble.com> you wrote:
> 
> On the other hand,  according to my basic understanding (Please correct me
> if I am wrong), U-boot can pass through the bootargs env variable
> information about available memory in the platform. For instance,  bootargs 
> mem=512M at 0xA0000000 .. instructs the kernel that the available memory is 512
> MB starting @ 0xA0000000, in such case the rest of the platform memory is
> not even visible to the kernel and its MMU. Is this conclusion true?

Actually, today we use the device tree to pass this information.

And it is not correct that any memory outside the specification of
"mem=" is not _visible_ to the kernel.  Please understand that it is
really up to the kernel (or whatever program you boot) to set up hiw
own memory map.  In case of the Linux, it is the Linux kernel itself
which implements the "mem=" ABI - and if you use it, it choses to
_ignore_ any other possibly existing memory regions.  But this is
totally voluntary, and done only in Linux.  There is nothing that
U-Boot does here, so the term "not visible" is only true in the sense
"because the kernel decides to close both eyes and never will even
attempt to look in that direction".

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
"In matters of principle, stand like a rock;  in  matters  of  taste,
swim with the current."                            - Thomas Jefferson

[U-Boot] Statically allocate a range of physical memory to an OS image.

[mazen.e]

Great, thank you very much for this valuable information.



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