[SeaBIOS] [PATCH] megasas: Add boot support for LSI MegaRAID SAS

[Gerd Hoffmann]

  Hi,

>> Although valid, it's not a good idea to use memalign_high for
>> temporary space.  One should use memalign_tmp for that purpose.
>>
> The thing here is that megasas_fire_cmd() is a generic function, so it
> needs to work in both 16 and 32-bit environs. So the frame pointer
> passed to this function needs to reference the same segment.

32-bit mode is relaxed, everything is a flat 32bit ptr and all those
funky segment/offset macros do basically nothing.

For 16-bit mode it is very important to get things right ...

> And this is where things get confused.
> I've converted the driver to use memalign_tmp() for allocating space for
> the frame. Which works.

The strategy ahci uses is to memalign_tmp() the data structures needed
for device probing, so they can easily freed in case the port is unused.
 When a drive is actually found (and registered) the memory for the data
structures is allocated again using memalign_low(), so it is permanently
available, accessible in 16-bit mode and the 16-bit only code paths
don't have to do any memory allocations when kicking transfers.

I think there are code paths where SET_LOWFLAT & friends are used for
memory allocated via memalign_tmp(), but that happens in 32bit mode only
where it doesn't really matter.

See ahci_port_realloc().

HTH,
  Gerd