When to use ioremap?

Jeff Garzik (jgarzik@pobox.com)
Sat, 24 Apr 1999 20:10:11 -0400 (EDT)

Hi guys,

Fresh from reading linux/Documentation/IO-mapping.txt (written by
Linus), I have a couple dumb questions that hopefully someone will

IO-mapping.txt describes reading from I/O space like
unsigned value = readl(0xc0000);
but it describes writing with ioremap().

Why does reading not require ioremap, while writing does?

And the file seems to imply that read/write[bwl] should be the sole way
to address I/O memory.

Why, then, does drivers/video/matroxfb.c have code for the case where
READx_WORKS is not true? Is this simply a performance optimization, or
a real requirement?



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