armv7 + lpae broken in 4.1.12+ ?
brad at heeltoe.com
Thu Nov 26 15:26:38 PST 2015
I was recently building a 4.1.12 kernel for a generic V7 platform with
LPAE. I could not get it to boot and then discovered two things:
- the early printk code in tty/serial call ioremap very early and it
fails because there's no heap
- the code in proc-v7-3level.S/cpu_v7_set_pte_ext doesn't work
The printk issue is no big deal. The pte issue is more important.
I found that the pte entries were garbage, which really confused me. I
finally discovered that the code in proc-v7-3level.S expects data in r0,
r2 & r3, but in fact it comes in on r0, r1 & r2.
My guess is that this is some vestige of the change made to
cpu_v7_switch_mm() some time ago to make the PA a 64 bit value (hence
using r0,r1). But this change was not made to cpu_v7_set_pte_ext, so it
lol. I guess I'm the only one who turns on LPAE for v7 cpu's...
The simple fix is to add "mov r3, r2; mov r2,r1" at the begining of
cpu_v7_set_pte_ext(), but that's a hack (but it does solve the problem
and the kernel boots).
I suspect the "right thing" is to make the prototype for
cpu_v7_set_pte_ext() in proc-fns.h use a phys_addr_t but I have not
tried that yet.
Can someone confirm that what I am seeing is correct?
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