So I have read the docs, peeked through the source and finally I'm
completely confused: What I want to do is access shared memory on the ISA
and/or PCI bus. Fine, readb() and friends are what I want. But what should
I feed them to be portable? A bus address or a virtual address? On i386
and most other architectures, both seem to work. From looking at
asm-mips/io.h, it looks like it _must_ be readb(bus_address). But then
most drivers happily use readb() et al. on ioremap()ed, i.e. virtual
addresses and even Linus himself does so, quoting him from
Documentation/IO-mapping.txt:
--[snip]--
char * baseptr = ioremap(0xFC000000, 1024*1024);
/* write a 'A' to the offset 10 of the area */
writeb('A',baseptr+10);
--[snap]--
Now I wonder what to do to get my driver as portable as possible. My best
guess at the moment is:
1. readb() and friends should get fed bus addresses only.
2. As ioremap() returns a virtual address, those addresses should get
dereferenced directly and Linus' example in IO-mapping.txt should get
fixed to "baseptr[10]='A';"
Is this correct?
Thanks for any insight,
Daniel.
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