PowerPC: _IO_BASE & friends

[Till Straumann]

Joel, I'd like to bring up an issue we talked about
a while ago, namely the definitions of

_IO_BASE etc. by libcpu/io.h.

>> Something else that bothers me are the definitions
>>
>> #define _IO_BASE        PREP_ISA_IO_BASE
>> #define _ISA_MEM_BASE   PREP_ISA_MEM_BASE
>> #define PCI_DRAM_OFFSET PREP_PCI_DRAM_OFFSET
>>
>> found in lib/libcpu/powerpc/shared/include/io.h
>>
>> This should be the business of the BSP rather than
>> the CPU library's!
>>
>Sounds reasonable to me also.  Could these be provided
>by the linker script? This is the most flexible and avoids
>the use of macros.
>
> -- joel
>
>> -- Till

These are my thoughts:

defining in bsp.h:

  +  more efficient
  +  more transparent
  -  existing code needs to be modified (include bsp.h in addition to
libcpu/io.h)
  -  macros should be avoided if possible

linkcmds:
  +  no macro needed
  +  existing source code needs no modification
  -  less efficient ("lis ry, _IO_BASE at ha; ori ry,ry,_IO_BASE at la; add
rx,rx,ry";
      using a macro expands to "addis rx,rx,_IO_BASE at ha")
  -  less transparent (hard to figure out for a reader where the symbol
is defined)

Going beyond _IO_BASE and _ISA_MEM_BASE: should there be a standard
way for rtems providing memory map info? How can an application or a
driver
figure out how to address a PCI or a VME location?

An example:

The mvme23xx BSP maps all PCI memory space into ISA memory. Hence,
to address a particular device on the mvme23xx, I use _ISA_MEM_BASE
+ pci_addr.
However, on a CHRP platform, PCI memory and ISA memory are disjoint.
There,
I might have to use pci_addr to address the same device. This makes it
complicated to port a driver between different RTEMS BSPs.

Worst of all, e.g. the libchip/dec21140 driver uses PREP_ISA_MEM_BASE to
address
pci memory space :-( which works fine on the mvme23xx but is likely
to fail if I try to use this driver for a PMC module on a different
board.

IMO, there is some work to be done in this area :-)


Comments?

-- Till.