bus: add driver for initializing the SSC bus on (some) qcom SoCs

Add bindings for the AHB bus which exposes the SSC (Snapdragon Sensor Core)
block in the global address space. This bus (and the SSC block itself) is
present on certain qcom SoCs.

In typical configuration, this bus (as some of the clocks and registers
that we need to manipulate) is not accessible to Linux, and the resources
on this bus are indirectly accessed by communicating with a hexagon CPU
core residing in the SSC block. In this configuration, the hypervisor is
the one performing the bus initialization for the purposes of bringing
the hexagon CPU core out of reset.

However, it is possible to change the configuration, in which case this
driver will initialize the bus.

In combination with drivers for resources on the SSC bus, this driver can
aid in debugging, and for example with a TLMM driver can be used to
directly access SSC-dedicated GPIO pins, removing the need to commit
to a particular usecase during hw design.

Finally, until open firmware for the hexagon core is available, this
approach allows for using sensors hooked up to SSC-dedicated GPIO pins
on mainline Linux simply by utilizing the existing in-tree drivers for
these sensors.
Signed-off-by: Michael Srba <Michael.Srba@seznam.cz>
Reviewed-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220411072156.24451-5-michael.srba@seznam.cz

drivers/bus/Kconfig

@@ -152,6 +152,17 @@ config QCOM_EBI2
 	  Interface 2, which can be used to connect things like NAND Flash,
 	  SRAM, ethernet adapters, FPGAs and LCD displays.
 
+config QCOM_SSC_BLOCK_BUS
+	bool "Qualcomm SSC Block Bus Init Driver"
+	  depends on ARCH_QCOM
+	  help
+	  Say y here to enable support for initializing the bus that connects
+	  the SSC block's internal bus to the cNoC (configurantion NoC) on
+	  (some) qcom SoCs.
+	  The SSC (Snapdragon Sensor Core) block contains a gpio controller,
+	  i2c/spi/uart controllers, a hexagon core, and a clock controller
+	  which provides clocks for the above.
+
 config SUN50I_DE2_BUS
 	bool "Allwinner A64 DE2 Bus Driver"
 	  default ARM64

drivers/bus/Makefile

@@ -25,6 +25,7 @@ obj-$(CONFIG_OMAP_INTERCONNECT)	+= omap_l3_smx.o omap_l3_noc.o
 
 obj-$(CONFIG_OMAP_OCP2SCP)	+= omap-ocp2scp.o
 obj-$(CONFIG_QCOM_EBI2)		+= qcom-ebi2.o
+obj-$(CONFIG_QCOM_SSC_BLOCK_BUS)	+= qcom-ssc-block-bus.o
 obj-$(CONFIG_SUN50I_DE2_BUS)	+= sun50i-de2.o
 obj-$(CONFIG_SUNXI_RSB)		+= sunxi-rsb.o
 obj-$(CONFIG_OF)		+= simple-pm-bus.o