<GSoC MMU project> Avoid translating attributes and move it from High-level to BSP code.

[Hesham Moustafa]

Hi,

Currently MMU attributes are defined at High-level code, So when
setting/changing it, that involves translating attributes to the BSP code
(low-level layer) to form a bit pattern that is compatible with cpu (
powerpc) attributes pattern for page table entry. The problem is we want to
avoid that translation and changing these attributes directly through BSP
layer only. I was thinking of some solutions and i will list it hoping to
get some feed backs.

1- The first solution is to create a type ( uint32_t ) for permissions, add
to this some functions like rtems_xxx_set_write, rtems_xxx_set_read_only
........... etc. These functions invokes BSP functions and it set bits
exactly mapping to the cpu page table bits. After that it can be ORed with
cpu page table attributes ( i.e setting some protection permissions ).

2- To create a dummy struct at high-level code that contains boolean fields
for each attribute may exist and provided by most HWs. So when
setting/unsetting attributes read this struct, collect "true" values, form
a bit pattern maps to cpu page table attributes bits and setting it. I
think this will solution will take longer time for checking true fields and
forming a bit pattern.

3- Create function that takes attribute type ( i.e READ_ONLY ) and boolean
parameter ( to determine whether to set/unset it ) and then change cpu page
table attributes bits according to parameters.

I would appreciate any other useful solutions.
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