bus: Add Baikal-T1 APB-bus driver

Baikal-T1 AXI-APB bridge is used to access the SoC subsystem CSRs.
IO requests are routed to this bus by means of the DW AMBA 3 AXI
Interconnect. In case if an attempted APB transaction stays with no
response for a pre-defined time an interrupt occurs and the bus gets
freed for a next operation. This driver provides the interrupt handler
to detect the erroneous address, prints an error message about the
address fault, updates an errors counter. The counter and the APB-bus
operations timeout can be accessed via corresponding sysfs nodes.
A dedicated sysfs-node can be also used to artificially cause the
bus errors described above.

[arnd: fix build warnings for missing includes and wrong return types]

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Serge Semin <[email protected]>
Cc: Alexey Malahov <[email protected]>
Cc: Paul Burton <[email protected]>
Cc: Olof Johansson <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Reported-by: kbuild test robot <[email protected]>
Reported-by: kbuild test robot <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

Author: fancer

drivers/bus/Kconfig

@@ -29,6 +29,21 @@ config BRCMSTB_GISB_ARB
 	  arbiter. This driver provides timeout and target abort error handling
 	  and internal bus master decoding.
 
+config BT1_APB
+	tristate "Baikal-T1 APB-bus driver"
+	depends on MIPS_BAIKAL_T1 || COMPILE_TEST
+	select REGMAP_MMIO
+	help
+	  Baikal-T1 AXI-APB bridge is used to access the SoC subsystem CSRs.
+	  IO requests are routed to this bus by means of the DW AMBA 3 AXI
+	  Interconnect. In case of any APB protocol collisions, slave device
+	  not responding on timeout an IRQ is raised with an erroneous address
+	  reported to the APB terminator (APB Errors Handler Block). This
+	  driver provides the interrupt handler to detect the erroneous
+	  address, prints an error message about the address fault, updates an
+	  errors counter. The counter and the APB-bus operations timeout can be
+	  accessed via corresponding sysfs nodes.
+
 config BT1_AXI
 	tristate "Baikal-T1 AXI-bus driver"
 	depends on MIPS_BAIKAL_T1 || COMPILE_TEST

drivers/bus/Makefile

@@ -13,6 +13,7 @@ obj-$(CONFIG_MOXTET)		+= moxtet.o
 # DPAA2 fsl-mc bus
 obj-$(CONFIG_FSL_MC_BUS)	+= fsl-mc/
 
+obj-$(CONFIG_BT1_APB)		+= bt1-apb.o
 obj-$(CONFIG_BT1_AXI)		+= bt1-axi.o
 obj-$(CONFIG_IMX_WEIM)		+= imx-weim.o
 obj-$(CONFIG_MIPS_CDMM)		+= mips_cdmm.o