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
--
Dr. Hannes Reinecke zSeries & Storage
[email protected] +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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