ARM: OMAP: simplify dmtimer context-loss handling

The context loss handling in dmtimer appears to assume that
omap_dm_timer_set_load_start() or omap_dm_timer_start() and
omap_dm_timer_stop() bracket all interactions.  Only the first two
restore the context and the last updates the context loss counter.
However omap_dm_timer_set_load() or omap_dm_timer_set_match() can
reasonably be called outside this bracketing, and the fact that they
call omap_dm_timer_enable() / omap_dm_timer_disable() suggest that
is expected.

So if, after a transition into and out of off-mode which would cause
the dm timer to loose all state, omap_dm_timer_set_match() is called
before omap_dm_timer_start(), the value read from OMAP_TIMER_CTRL_REG
will be 'wrong' and this wrong value will be stored context.tclr so
a subsequent omap_dm_timer_start() can fail (As the control register
is wrong).

Simplify this be doing the restore-from-context in
omap_dm_timer_enable() so that whenever the timer is enabled, the
context is correct. Also update the ctx_loss_count at the same time as
we notice it is wrong - these is no value in delaying this until the
omap_dm_timer_disable() as it cannot change while the timer is enabled.

Signed-off-by: NeilBrown <neilb@suse.de>
[jon-hunter@ti.com: minor update to subject and changed variable name]
Signed-off-by: Jon Hunter <jon-hunter@ti.com>
ARM: OMAP: Add function to request timer by node

Add a function so that OMAP dmtimers can be requested by device-tree
node. This allows for devices, such as the internal DSP, or drivers,
such as PWM, to reference a specific dmtimer node via the device-tree.

Given that there are several APIs available for requesting dmtimers
(by ID, by capability or by node) consolidate the code for all these
functions into a single helper function that can be used by these
request functions.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
ARM: OMAP: Force dmtimer restore if context loss is not detectable

When booting with device-tree the function pointer for detecting context
loss is not populated. Ideally, the pm_runtime framework should be
enhanced to allow a means for reporting context/state loss and we could
avoid populating such function pointers altogether. In the interim until
a generic non-device specific solution is in place, force a restore of
the dmtimer when enabling the timer. Also add a warning during probe to
warn that context loss cannot be detected.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Merge branch 'omap-dmtimer-for-v3.10' into omap-daily-testing