OpenRISC borrows its timer sync logic from MIPS, Matt helped to review
the OpenRISC implementation and noted that we may suffer the same
deadlock case that MIPS has faced. The case being:
"the MIPS timer synchronization code contained the possibility of
deadlock. If you mark a CPU online before it goes into the synchronize
loop, then the boot CPU can schedule a different thread and send IPIs to
all "online" CPUs. It gets stuck waiting for the secondary to ack it's
IPI, since this secondary CPU has not enabled IRQs yet, and is stuck
waiting for the master to synchronise with it. The system then
deadlocks."
Fix this by moving set_cpu_online() to after timer sync.
Reported-by: Matt Redfearn <matt.redfearn@mips.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>
In case timers are not in sync when cpus start (i.e. hot plug / offset
resets) we need to synchronize the secondary cpus internal timer with
the main cpu. This is needed as in OpenRISC SMP there is only one
clocksource registered which reads from the same ttcr register on each
cpu.
This synchronization routine heavily borrows from mips implementation that
does something similar.
Signed-off-by: Stafford Horne <shorne@gmail.com>
On OpenRISC the icache does not snoop data stores. This can cause
aliasing as reported by Jan. This patch fixes the issue to ensure icache
is properly synchronized when code is written to memory. It supports both
SMP and UP flushing.
This supports dcache flush as well for architectures that do not support
write-through caches; most OpenRISC implementations do implement
write-through cache however. Dcache flushes are done only on a single
core as OpenRISC dcaches all support snooping of bus stores.
Signed-off-by: Jan Henrik Weinstock <jan.weinstock@ice.rwth-aachen.de>
[shorne@gmail.com: Squashed patches and wrote commit message]
Signed-off-by: Stafford Horne <shorne@gmail.com>
Currently we do a spin on secondary cpus when waiting to boot. This
theoretically causes issues with power consumption and does cause issues
with qemu cycle burning (it starves cpu 0 from actually being able to
boot.)
This change puts each secondary cpu to sleep if they have a power
management unit, then signals them to wake via IPI when its time to boot.
If the cpus have no power management unit they will loop as before.
Note: The wakeup IPI requires a special interrupt handler as on secondary
cpu's the interrupt infrastructure is not yet established. This
interrupt handler is set and reset by updating SPR_EVBAR.
Signed-off-by: Stafford Horne <shorne@gmail.com>
During SMP testing we were getting the below warning after booting the
secondary cpu:
[ 0.060000] BUG: scheduling while atomic: swapper/1/0/0x00000000
This change follows similar patterns from other architectures to start
the schduler with preempt disabled.
Signed-off-by: Stafford Horne <shorne@gmail.com>
This patch introduces the SMP support for the OpenRISC architecture.
The SMP architecture requires cores which have multi-core features which
have been introduced a few years back including:
- New SPRS SPR_COREID SPR_NUMCORES
- Shadow SPRs
- Atomic Instructions
- Cache Coherency
- A wired in IPI controller
This patch adds all of the SMP specific changes to core infrastructure,
it looks big but it needs to go all together as its hard to split this
one up.
Boot loader spinning of second cpu is not supported yet, it's assumed
that Linux is booted straight after cpu reset.
The bulk of these changes are trivial changes to refactor to use per cpu
data structures throughout. The addition of the smp.c and changes in
time.c are the changes. Some specific notes:
MM changes
----------
The reason why this is created as an array, and not with DEFINE_PER_CPU
is that doing it this way, we'll save a load in the tlb-miss handler
(the load from __per_cpu_offset).
TLB Flush
---------
The SMP implementation of flush_tlb_* works by sending out a
function-call IPI to all the non-local cpus by using the generic
on_each_cpu() function.
Currently, all flush_tlb_* functions will result in a flush_tlb_all(),
which has always been the behaviour in the UP case.
CPU INFO
--------
This creates a per cpu cpuinfo struct and fills it out accordingly for
each activated cpu. show_cpuinfo is also updated to reflect new version
information in later versions of the spec.
SMP API
-------
This imitates the arm64 implementation by having a smp_cross_call
callback that can be set by set_smp_cross_call to initiate an IPI and a
handle_IPI function that is expected to be called from an IPI irqchip
driver.
Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
[shorne@gmail.com: added cpu stop, checkpatch fixes, wrote commit message]
Signed-off-by: Stafford Horne <shorne@gmail.com>
Stafford Horne
Jan Henrik Weinstock
Stefan Kristiansson