xics: Disable endianness swapping

The endianess swapping code caused the core to diverge from microwatt resulting in:
- The xics tests not working as-is: https://github.com/antonblanchard/microwatt/blob/master/tests/xics/xics.h
- byte writes writing to the incorrect byte

This removes endianswapping and minimizes the delta from upstream for the xics irq.h header.

litex/soc/cores/cpu/microwatt/core.py

@@ -123,7 +123,6 @@ class Microwatt(CPU):
                 variant      = self.variant,
                 core_irq_out = self.core_ext_irq,
                 int_level_in = self.interrupt,
-                endianness   = self.endianness
             )
             xicsicp_region = soc_region_cls(origin=soc.mem_map.get("xicsicp"), size=4096, cached=False)
             xicsics_region = soc_region_cls(origin=soc.mem_map.get("xicsics"), size=4096, cached=False)
@@ -212,22 +211,12 @@ class Microwatt(CPU):
 
 
 class XICSSlave(Module, AutoCSR):
-    def __init__(self, platform, core_irq_out=Signal(), int_level_in=Signal(16), endianness="big", variant="standard"):
+    def __init__(self, platform, core_irq_out=Signal(), int_level_in=Signal(16), variant="standard"):
         self.variant = variant
 
         self.icp_bus    = icp_bus    = wishbone.Interface(data_width=32, adr_width=12)
         self.ics_bus    = ics_bus    = wishbone.Interface(data_width=32, adr_width=12)
 
-        # Bus endianness handlers
-        self.icp_dat_w = Signal(32)
-        self.icp_dat_r = Signal(32)
-        self.comb += self.icp_dat_w.eq(icp_bus.dat_w if endianness == "big" else reverse_bytes(icp_bus.dat_w))
-        self.comb += icp_bus.dat_r.eq(self.icp_dat_r if endianness == "big" else reverse_bytes(self.icp_dat_r))
-        self.ics_dat_w = Signal(32)
-        self.ics_dat_r = Signal(32)
-        self.comb += self.ics_dat_w.eq(ics_bus.dat_w if endianness == "big" else reverse_bytes(ics_bus.dat_w))
-        self.comb += ics_bus.dat_r.eq(self.ics_dat_r if endianness == "big" else reverse_bytes(self.ics_dat_r))
-
         # XICS signals
         self.ics_icp_xfer_src = Signal(4)
         self.ics_icp_xfer_pri = Signal(8)
@@ -238,11 +227,11 @@ class XICSSlave(Module, AutoCSR):
             i_rst            = ResetSignal(),
 
             # Wishbone bus
-            o_wishbone_dat_r = self.icp_dat_r,
+            o_wishbone_dat_r = icp_bus.dat_r,
             o_wishbone_ack   = icp_bus.ack,
 
             i_wishbone_adr   = icp_bus.adr,
-            i_wishbone_dat_w = self.icp_dat_w,
+            i_wishbone_dat_w = icp_bus.dat_w,
             i_wishbone_cyc   = icp_bus.cyc,
             i_wishbone_stb   = icp_bus.stb,
             i_wishbone_sel   = icp_bus.sel,
@@ -260,11 +249,11 @@ class XICSSlave(Module, AutoCSR):
             i_rst            = ResetSignal(),
 
             # Wishbone bus
-            o_wishbone_dat_r = self.ics_dat_r,
+            o_wishbone_dat_r = ics_bus.dat_r,
             o_wishbone_ack   = ics_bus.ack,
 
             i_wishbone_adr   = ics_bus.adr,
-            i_wishbone_dat_w = self.ics_dat_w,
+            i_wishbone_dat_w = ics_bus.dat_w,
             i_wishbone_cyc   = ics_bus.cyc,
             i_wishbone_stb   = ics_bus.stb,
             i_wishbone_sel   = ics_bus.sel,

litex/soc/cores/cpu/microwatt/irq.h

@@ -33,6 +33,8 @@ void isr(uint64_t vec);
 // Default external interrupt priority set by software during IRQ enable
 #define PPC_EXT_INTERRUPT_PRIO	0x08
 
+#define bswap32(x) (uint32_t)__builtin_bswap32((uint32_t)(x))
+
 static inline uint8_t xics_icp_readb(int reg)
 {
 	return *((uint8_t*)(XICSICP_BASE + reg));
@@ -45,22 +47,22 @@ static inline void xics_icp_writeb(int reg, uint8_t value)
 
 static inline uint32_t xics_icp_readw(int reg)
 {
-	return *((uint32_t*)(XICSICP_BASE + reg));
+	return bswap32(*((uint32_t*)(XICSICP_BASE + reg)));
 }
 
 static inline void xics_icp_writew(int reg, uint32_t value)
 {
-	*((uint32_t*)(XICSICP_BASE + reg)) = value;
+	*((uint32_t*)(XICSICP_BASE + reg)) = bswap32(value);
 }
 
 static inline uint32_t xics_ics_read_xive(int irq_number)
 {
-	return *((uint32_t*)(XICSICS_BASE + 0x800 + (irq_number << 2)));
+	return bswap32(*((uint32_t*)(XICSICS_BASE + 0x800 + (irq_number << 2))));
 }
 
 static inline void xics_ics_write_xive(int irq_number, uint32_t priority)
 {
-	*((uint32_t*)(XICSICS_BASE + 0x800 + (irq_number << 2))) = priority;
+	*((uint32_t*)(XICSICS_BASE + 0x800 + (irq_number << 2))) = bswap32(priority);
 }
 
 static inline void mtmsrd(uint64_t val)