linux-phytec-ti

remoteproc/pruss_soc: fix system suspend/MStandby config issues

The PRU-ICSS subsystem has a separate PRUSS_CFG module that
contains various configuration registers. This includes a control
bit STANDBY_INIT in register PRUSS_CFG register to initiate a
Standby sequence (when set) and trigger a MStandby request to the
SoC's PRCM module. This same bit is also used to enable the OCP
master ports (when cleared). The system suspend/resume functionality
on AM33xx/AM437x/AM57xx SoCs requires all initiators to assert their
MStandby signal properly inorder to successfully enter suspend, and
resume on a wakeup event.

Certain firmwares can enable the OCP master ports through the
STANDBY_INIT programming on the firmware side in order to access
peripherals or memories external to the PRUSS. This causes a hang
in the resume sequence on AM33xx/AM437x boards and requires a
board reset to come out of the hang.

This patch adds the preliminary System PM callbacks in the PRUSS SoC
bus driver, and fixes this system resume hang by setting the
STANDBY_INIT in the PM system suspend callback and resetting it back
in the PM system resume callback, if so configured. The clearing of
the STANDBY_INIT during resume requires an acknowledgment from PRCM
and is done through the monitoring of the PRUSS_SYSCFG.SUB_MWAIT bit.

NOTE:
1. This patch only adds the PM callbacks with code to fix the System
   Suspend/Resume hang issue on AM33xx/AM437x SoCs, but does not
   implement the full context save and restore required for the PRUSS
   drivers to work across system suspend/resume when the power domain
   is switched off (L4PER domain is switched OFF on AM335x/AM437x
   during system suspend/resume, so PRUSS modules do lose context).
2. The PRUSS driver functionality on AM57xx SoCs is not affected that
   much because the PER power domain to which the PRUSS IPs belong is
   not switched OFF during suspend/resume.

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