ARM: imx: avic: set low-power interrupt mask for imx25

ARM: imx: avic: set low-power interrupt mask for imx25

imx25 contains two registers (LPIMR0 and 1) to define which interrupts
are enabled in low-power mode. As of today, those two registers are
configured to enable all interrupts. Before going to low-power mode, the
AVIC's INTENABLEH and INTENABLEL registers are configured to enable only
those interrupts which are used as wakeup sources.

It turned out that this approach is not sufficient if we want the imx25
to go into stop mode during suspend-to-ram. (Stop mode is the low-power
mode that consumes the least power. The peripheral master clock is
switched off in this mode). For stop mode to work, the LPIMR0 and 1
registers have to be configured with the set of interrupts that are
allowed in low-power mode. Fortunately, the bits in the LPIMR registers
are assigned to the same interrupts as the bits in INTENABLEH and
INTENABLEL. However, LPIMR uses 1 to mask an interrupt whereas the
INTENABLE registers use 1 to enable an interrupt.

This patch sets the LPIMR registers to the inverted bitmask of the
INTENABLE registers during suspend and goes back to "all interrupts
masked" when we wake up again. We also make this the default at startup.

As far as I know, the other supported imx architectures have no similar
mechanism. Since the LPIMR registers are part of the CCM module, we
query the device tree for an imx25 ccm node in order to detect if we're
running on imx25.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>