linux-phytec-ti

remoteproc/omap: request a timer(s) for remoteproc usage

The remote processors in OMAP4+ SoCs are equipped with internal
timers, like the internal SysTick timer in a Cortex M3/M4 NVIC or
the CTM timer within Unicache in IPU & DSP. However, these timers
are gated when the processor subsystem clock is gated, making
them rather difficult to use as OS tick sources. They will not
be able to wakeup the processor from any processor-sleep induced
clock-gating states.

This can be avoided by using an external timer as the tick source,
which can be controlled independently by the core remoteproc
driver code, but still allowing the processor subsystem clock to
be auto-gated when the remoteproc cores are idle.

This patch adds the support for remote processors to request a
timer(s) to be used by the remoteproc. The timers are enabled and
disabled in line with the enabling/disabling of the remoteproc.
The timer data is not mandatory if the advanced device management
features are not required.

The current design relies on OMAP DMTimer API, which is limited
to only the OMAP machine-specific layers in arch/arm, so the logic
is implemented through OMAP rproc specific platform data ops. The
OMAP remoteproc driver mainly requires ops to request/free a dmtimer,
and to start/stop a timer. The split API helps in controlling the
timer state without having to request and release a timer everytime
it needs to use the timer. The required pdata ops implementations
have also been added along with the core timer support. These
functions need to be supplied to the OMAP remoteproc driver through
the pdata quirks.

This timer support logic needs to be revisited as and when the dmtimer
code moves under the /drivers folder.

NOTE: If the gptimer is already in use by the time IPU and/or
DSP are loaded, the processors will fail to boot.

Signed-off-by: Suman Anna <s-anna@ti.com>