On Thu, Oct 04, 2012 at 09:19:04PM +1000, Benjamin Herrenschmidt wrote:
On Sun, 2012-09-30 at 17:28 -0600, Jason Gunthorpe wrote:
quoted
asm/page.h discusses the calculation for v2p and p2v, it should be:
va = pa + KERNELBASE - PHYSICAL_START
which is the same as:
va = pa + LOAD_OFFSET
tophys/tovirt were using PAGE_OFFSET, which as page.h says, is almost
always the same thing.
Signed-off-by: Jason Gunthorpe <redacted>
It's a bit gross tho in that KERNEL_BASE, PHYSICAL_START and LOAD_OFFSET
are about where the kernel is linked/running, and while the value ends
up happening to also be the p->v offset (and indeed not by accident), it
makes the code less clear and more confusing.
Yes, I found the three names confusing.. However LOAD_OFFSET is the
name that include/asm-generic/vmlinux.lds.h and many arch's use for
P2V translation in the linker script, so at least there is some
precedent.
I don't have the bandwidth to revisit all that, but I really think that
whole are area where PAGE_OFFSET doesn't map 0 needs revisiting.
Something like that is also outside my scope.. This patch does fix a
bug I hit when CONFIG_PHYSICAL_START is used, are there problems with
it in other cases?
FWIW, this is part of a larger work that makes CONFIG_PHYSICAL_START
work on PPC404, which is not yet clean enough to post:
https://github.com/jgunthorpe/linux/commit/90df2d247c9db5d39c32dbbada0815f15d7b3be7
Regards,
Jason