Properly managing sub-allocations

[M. Warner Losh]

In message: <200610021620.44185.john at baldwin.cx>
            John Baldwin <john at baldwin.cx> writes:
: On Monday 02 October 2006 15:42, M. Warner Losh wrote:
: > In message: <200610021403.50339.john at baldwin.cx>
: >             John Baldwin <john at baldwin.cx> writes:
: > : > However, this may break some existing drivers that allocate a BAR,
: > : > peek at its type and then either activate it or allocate another
: > : > BAR...  The TAG is valid, but the handle isn't.
: > : 
: > : They generally peak at the BAR register itself though, not the value of 
: > : rman_get_bustag() though, right?
: > 
: > Some do, some get the resource and look at it.  There's a lot of
: > variance here.  Do you put knowledge of how to decode PCI bars into
: > every driver, or do you let the pci bus take care of it?  Since the
: > knowledge is nearly trivial, different people decide differenly.  It
: > is still a technique that has been used, and you'll need to be careful
: > to make sure you don't break anything.  After all, 0 is a valid I/O
: > tag and it is also the default value...
: 
: Err, how can code examine the actual bus tag value of a non-active resource?  
: By definition it's set an opaque MD value.  You can't compare it against 
: SYS_RES_MEMORY for example.  On i386 systems it happens to be an int, on some 
: other systems (alpha maybe?) I think it can be a pointer to a structure of 
: function pointers for the different bus space operations.  I don't think any 
: MI code should ever be examining the bus tag or handle except to pass them as 
: opaque parameters to bus_space_*().

Actually, you are right.  I'm confusing success/failure of allocating
a I/O and/or Memory bar with this...

Warner