ARM: suspend: use hash of cpu_logical_map value to index into save array

Currently we hash the MPIDR of the CPU being suspended to determine which
entry in the sleep_save_sp array to use. In some situations, such as when
we want to resume on another physical CPU, the MPIDR of another CPU should
be used instead.

So let's use the value of cpu_logical_map(smp_processor_id()) in place
of the MPIDR in the suspend path.  This will result in the same index
being used as with the previous code unless the caller has modified
cpu_logical_map() beforehand with the MPIDR of the physical CPU the
suspending logical CPU will resume on.

Consequently, if doing a physical CPU migration, cpu_logical_map() must
be updated appropriately somewhere between cpu_pm_enter() and
cpu_suspend().

The register allocation in __cpu_suspend is reworked in order to better
accommodate the additional argument.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
ARM: gic: add CPU migration support

This is required by the big.LITTLE switcher code.

The gic_migrate_target() changes the CPU interface mapping for the
current CPU to redirect SGIs to the specified interface, and it also
updates the target CPU for each interrupts to that CPU interface
if they were targeting the current interface.  Finally, pending
SGIs for the current CPU are forwarded to the new interface.

Because Linux does not use it, the SGI source information for the
forwarded SGIs is not preserved.  Neither is the source information
for the SGIs sent by the current CPU to other CPUs adjusted to match
the new CPU interface mapping.  The required registers are banked so
only the target CPU could do it.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: b.L: core switcher code

This is the core code implementing big.LITTLE switcher functionality.
Rationale for this code is available here:

http://lwn.net/Articles/481055/

The main entry point for a switch request is:

void bL_switch_request(unsigned int cpu, unsigned int new_cluster_id)

If the calling CPU is not the wanted one, this wrapper takes care of
sending the request to the appropriate CPU with schedule_work_on().

At the moment the core switch operation is handled by bL_switch_to()
which must be called on the CPU for which a switch is requested.

What this code does:

  * Return early if the current cluster is the wanted one.

  * Close the gate in the kernel entry vector for both the inbound
    and outbound CPUs.

  * Wake up the inbound CPU so it can perform its reset sequence in
    parallel up to the kernel entry vector gate.

  * Migrate all interrupts in the GIC targeting the outbound CPU
    interface to the inbound CPU interface, including SGIs. This is
    performed by gic_migrate_target() in drivers/irqchip/irq-gic.c.

  * Call cpu_pm_enter() which takes care of flushing the VFP state to
    RAM and save the CPU interface config from the GIC to RAM.

  * Modify the cpu_logical_map to refer to the inbound physical CPU.

  * Call cpu_suspend() which saves the CPU state (general purpose
    registers, page table address) onto the stack and store the
    resulting stack pointer in an array indexed by the updated
    cpu_logical_map, then call the provided shutdown function.
    This happens in arch/arm/kernel/sleep.S.

At this point, the provided shutdown function executed by the outbound
CPU ungates the inbound CPU. Therefore the inbound CPU:

  * Picks up the saved stack pointer in the array indexed by its MPIDR
    in arch/arm/kernel/sleep.S.

  * The MMU and caches are re-enabled using the saved state on the
    provided stack, just like if this was a resume operation from a
    suspended state.

  * Then cpu_suspend() returns, although this is on the inbound CPU
    rather than the outbound CPU which called it initially.

  * The function cpu_pm_exit() is called which effect is to restore the
    CPU interface state in the GIC using the state previously saved by
    the outbound CPU.

  * Exit of bL_switch_to() to resume normal kernel execution on the
    new CPU.

However, the outbound CPU is potentially still running in parallel while
the inbound CPU is resuming normal kernel execution, hence we need
per CPU stack isolation to execute bL_do_switch().  After the outbound
CPU has ungated the inbound CPU, it calls mcpm_cpu_power_down() to:

  * Clean its L1 cache.

  * If it is the last CPU still alive in its cluster (last man standing),
    it also cleans its L2 cache and disables cache snooping from the other
    cluster.

  * Power down the CPU (or whole cluster).

Code called from bL_do_switch() might end up referencing 'current' for
some reasons.  However, 'current' is derived from the stack pointer.
With any arbitrary stack, the returned value for 'current' and any
dereferenced values through it are just random garbage which may lead to
segmentation faults.

The active page table during the execution of bL_do_switch() is also a
problem.  There is no guarantee that the inbound CPU won't destroy the
corresponding task which would free the attached page table while the
outbound CPU is still running and relying on it.

To solve both issues, we borrow some of the task space belonging to
the init/idle task which, by its nature, is lightly used and therefore
is unlikely to clash with our usage.  The init task is also never going
away.

Right now the logical CPU number is assumed to be equivalent to the
physical CPU number within each cluster. The kernel should also be
booted with only one cluster active.  These limitations will be lifted
eventually.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: add clockevent save/restore support

Per-CPU timers that are shutdown when a CPU is switched over must be disabled
upon switching and reprogrammed on the inbound CPU by relying on the
clock events management API. save/restore sequence is executed with irqs
disabled as mandated by the clock events API.

The next_event is an absolute time, hence, when the inbound CPU resumes,
if the timer has expired the min delta is forced into the tick device to
fire after few cycles.

This patch adds switching support for clock events that are per-CPU and
have to be migrated when a switch takes place; the cpumask of the clock
event device is checked against the cpumask of the current cpu, and if
they match, the clockevent device mode is saved and it is put in
shutdown mode. Resume code reprogrammes the tick device accordingly.

Tested on A15/A7 fast models and architected timers.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: move to dedicated threads rather than workqueues

The workqueues are problematic as they may be contended.
They can't be scheduled with top priority either.  Also the optimization
in bL_switch_request() to skip the workqueue entirely when the target CPU
and the calling CPU were the same didn't allow for bL_switch_request() to
be called from atomic context, as might be the case for some cpufreq
drivers.

Let's move to dedicated kthreads instead.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: simplify stack isolation

We now have a dedicated thread for each logical CPU.  That's plenty
of stack space for our needs.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: hot-unplug half of the available CPUs

In a regular kernel configuration, all the CPUs are initially available.
But the switcher execution model uses half of them at any time.  Instead
of hacking the DTB to remove half of the CPUs, let's remove them at
run time and make sure we still have a working switcher configuration.
This way, the same DTB can be used whether or not the switcher is used.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: do not hardcode GIC IDs in the code

Currently, GIC IDs are hardcoded making the code dependent on the 4+4 b.L
configuration.  Let's allow for GIC IDs to be discovered upon switcher
initialization to support other b.L configurations such as the 1+1 one,
or 2+3 as on the VExpress TC2.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: ability to enable and disable the switcher via sysfs

The /sys/kernel/bL_switcher/enable file allows to enable or disable
the switcher by writing 1 or 0 to it respectively.  It is still enabled
by default on boot.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: add kernel cmdline param to disable the switcher on boot

By adding no_bL_switcher to the kernel cmdline string, the switcher
won't be activated automatically at boot time.  It is still possible
to activate it later with:

	echo 1 > /sys/kernel/bL_switcher/active

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: remove assumptions between logical and physical CPUs

Up to now, the logical CPU was somehow tied to the physical CPU number
within a cluster.  This causes problems when forcing the boot CPU to be
different from the first enumerated CPU in the device tree creating a
discrepancy between logical and physical CPU numbers.

Let's make the pairing completely independent from physical CPU numbers.

Let's keep only those logical CPUs with same initial CPU cluster to create
a uniform scheduler profile without having to modify any of the probed
topology and compute capacity data.  This has the potential to create
a non contiguous CPU numbering space when the switcher is active with
potential impact on buggy user space tools.  It is however better to fix
those tools rather than making the switcher code more intrusive.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
ARM: bL_switcher: filter CPU hotplug requests when the switcher is active

Trying to support both the switcher and CPU hotplug at the same time
is tricky due to ambiguous semantics.  So let's at least prevent users
from messing around with those logical CPUs the switcher has removed
and those which were not active when the switcher was activated.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: add a simple /dev user interface for debugging purposes

Only the basic call to aid debugging.

*** NOT FOR PRODUCTION ***

Usage:

	echo <cpuid>,<clusterid> > /dev/b.L_switcher

where <cpuid> is the logical CPU number, and <clusterid> is 0 for the
first cluster and 1 for the second cluster.

Signed-off-by: nicolas Pitre <nico@linaro.org>
Merge branch 'iks_for_rmk' of git://git.linaro.org/people/nico/linux into devel-stable

Nicolas Pitre writes:

This is the first part of the patch series adding IKS (In-Kernel
Switcher) support for big.LITTLE system architectures.  This consists of
the core patches only.  Extra patches to come later will introduce
various optimizations and tracing support.

Those patches were posted on the list a while ago here:

   http://news.gmane.org/group/gmane.linux.ports.arm.kernel/thread=253942
ARM: 7831/1: mmc: mmci: Adapt to new pinctrl handling

There is no need for every driver to fetch a pinctrl handle and to
select the default state. Instead this is handled by the device driver
core, thus we can remove this piece of code from mmci.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
ARM: 7832/1: mmc: mmci: Use optional sleep pinctrl state

By optionally putting the pins into sleep state in the .runtime_suspend
callback we can accomplish two things. One is to minimize current leakage
from pins and thus save power, second we can prevent the IP from driving
pins output in an uncontrolled manner, which may happen if the power domain
drops the domain regulator.

When returning from idle, entering .runtime_resume callback, the pins
are restored to default state.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Rickard Andersson <rickard.andersson@stericsson.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
ARM: 7833/1: mmc: mmci: Adapt to register write restrictions

After a write to the MMCICLOCK register data cannot be written to this
register for three feedback clock cycles. Writes to the MMCIPOWER
register must be separated by three MCLK cycles. Previously no issues
has been observered, but using higher ARM clock frequencies on STE-
platforms has triggered this problem.

The MMCICLOCK register is written to in .set_ios and for some data
transmissions for SDIO. We do not need a delay at the data transmission
path, because sending and receiving data will require more than three
clock cycles. Then we use a simple logic to only delay in .set_ios and
thus we don't affect throughput performance.

Signed-off-by: Johan Rudholm <jrudholm@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Rickard Andersson <rickard.andersson@stericsson.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
ARM: 7834/1: mmc: mmci: Save and restore register context

If a corresponding power domain exists for the device and it manages
to cut the domain regulator while the device is runtime suspended,
the IP loses it's registers context. We restore the context in the
.runtime_resume callback from the existing register caches to adapt
to this situation.

We also want to make sure the registers are in a known state while
restoring context in the case when the power domain did not drop the
power, since there are restrictions for the order of writing to these
registers. To handle this, we clear the registers in the
.runtime_suspend callback.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Rickard Andersson <rickard.andersson@stericsson.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
ARM: bL_switcher: Add synchronous enable/disable interface

Some subsystems will need to know for sure whether the switcher is
enabled or disabled during certain critical regions.

This patch provides a simple mutex-based mechanism to discover
whether the switcher is enabled and temporarily lock out further
enable/disable:

  * bL_switcher_get_enabled() returns true iff the switcher is
    enabled and temporarily inhibits enable/disable.

  * bL_switcher_put_enabled() permits enable/disable of the switcher
    again after a previous call to bL_switcher_get_enabled().

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
ARM: bL_switcher: Add runtime control notifier

Some subsystems will need to respond synchronously to runtime
enabling and disabling of the switcher.

This patch adds a dedicated notifier interface to support such
subsystems.  Pre- and post- enable/disable notifications are sent
to registered callbacks, allowing safe transition of non-b.L-
transparent subsystems across these control transitions.

Notifier callbacks may veto switcher (de)activation on pre notifications
only.  Post notifications won't revert the action.

If enabling or disabling of the switcher fails after the pre-change
notification has been sent, subsystems which have registered
notifiers can be left in an inappropriate state.

This patch sends a suitable post-change notification on failure,
indicating that the old state has been reestablished.

For example, a failed initialisation will result in the following
sequence:

    BL_NOTIFY_PRE_ENABLE
    /* switcher initialisation fails */
    BL_NOTIFY_POST_DISABLE

It is the responsibility of notified subsystems to respond in an
appropriate way.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>