On 11/13/2012 09:01 AM, Gerd Hoffmann wrote:
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().
Ah. Thanks for the explanation.
I've converted it now to use memalign_tmplow(), so everybody should be happy.
Cheers,
Hannes