Highmem support on ppc32 plattform with PREEMPT_RT_FULL option

Highmem support on ppc32 plattform with PREEMPT_RT_FULL option

[Heiko Schumann]

Hello,

i´ve a ppc32 processor with 2 GB Ram. I use a 3.8.4 Kernel with vendor
and 3.8.4rt2 patch. To support  2 GB of RAM i´ve to set the kernel
option HIGHMEM. But this option is not available when PREEMPT_RT_FULL
is selected.
Is there a workaround or additional patch to use more than 1GB RAM on
a ppc32 with the option PREEMPT_RT_FULL?

Thanks
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Re: Highmem support on ppc32 plattform with PREEMPT_RT_FULL option

[Sebastian Andrzej Siewior]

* Heiko Schumann | 2013-05-14 13:04:34 [+0200]:

>Hello,
Hi,

>i´ve a ppc32 processor with 2 GB Ram. I use a 3.8.4 Kernel with vendor
>and 3.8.4rt2 patch. To support  2 GB of RAM i´ve to set the kernel
>option HIGHMEM. But this option is not available when PREEMPT_RT_FULL
>is selected.
>Is there a workaround or additional patch to use more than 1GB RAM on
>a ppc32 with the option PREEMPT_RT_FULL?

No, we have only arm and x86 so far. Either try to do the same thing on
Power that has been on ARM & x86.
A workaround would be to adjust lowmem, virtual base and user stack.
That means your userland wouldn't have 3GiB virtual address space but
the kernel could access 2GiB.
Something like 
  CONFIG_PAGE_OFFSET=0x40000000
  CONFIG_KERNEL_START=0x40000000
  CONFIG_TASK_SIZE=0x40000000

should work.

>
>Thanks

Sebatian
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