ip26_ucmem(D3)ip26_ucmem(D3)NAME
ip26_enable_ucmem, ip26_return_ucmem - change memory mode on IP26 or IP28
processor
SYNOPSIS
#include <sys/systm.h>
ulong ip26_enable_ucmem(void);
void ip26_return_ucmem(ulong oldstate);
Arguments
oldstate Previous memory mode. (Only ip26_return_ucmem has an input
argument.)
DESCRIPTION
The IP26 motherboard (Power Indigo2, Indigo2 10000, Power Challenge M)
has 2 memory setup modes. These modes only affect CPU accesses to main
memory. They have no impact on CPU accesses to device registers (PIOs),
or on DMA between devices and main memory. One of the modes (the
default) is set up to allow CPU accesses to main memory to occur as fast
as possible, but restricts the CPU from making uncached writes to main
memory. The other mode is set up to allow any CPU accesses to main
memory (cached or uncached), but slows down CPU accesses to main memory.
If a driver makes uncached writes to main memory without having
previously called ip26_enable_ucmem, it will crash the system.
The ip26_enable_ucmem function allows the processor to perform uncached
writes to main memory. During the interval between calling
ip26_enable_ucmem and ip26_return_ucmem, all processor accesses to main
memory (cached or uncached) perform slower. Therefore, use of this
function is recommended only if the device driver is unable for some
reason to use cached accesses, and cache coherency operations. (See the
dki_dcache_*(D3) routines.) The value returned from ip26_enable_ucmem
must be saved and passed as the argument to a following call to
ip26_return_ucmem.
The ip26_return_ucmem returns the memory mode to its state from before
the matching call to ip26_enable_ucmem. These functions are designed to
always be used as a matched pair, in which a driver enables uncached
writes, performs the writes, and then returns the memory system to its
previous mode. The reason for using ip26_return_ucmem instead of a
function which simply disallows uncached writes is that it is possible to
have an interrupt service routine which needs to do uncached accesses.
This can lead to a scenario where a driver top-half enables uncached
writes, but before performing all the writes gets interrupted. The
interrupt service routine could then enable uncached writes, perform its
writes, and then disable uncached writes. Upon return from the ISR, the
driver top-half would then attempt to perform uncached writes, and crash
the system.
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ip26_ucmem(D3)ip26_ucmem(D3)
The ip26_enable_ucmem and ip26_return_ucmem functions are only necessary
for drivers which run on IP26 or IP28 processors, but stubs are provided
for other architectures so that driver binaries will function across
platforms.
Return Values
The ip26_enable_ucmem function returns the previous memory system mode.
This must then be passed in as the argument to the matching call to
ip26_return_ucmem.
Synchronization Considerations
The ip26_enable_ucmem and ip26_return_ucmem functions do not sleep, so
they are callable from anywhere in a device driver.
See Also
dki_dcache_inval(D3X), dki_dcache_wb(D3X), dki_dcache_wbinval(D3X)
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