ARCv2: don't assume core 0x54 has dual issue

The first release of core4 (0x54) was dual issue only (HS4x).
Newer releases allow hardware to be configured as single issue (HS3x)
or dual issue.

Prevent accessing a HS4x only aux register in HS3x, which otherwise
leads to illegal instruction exceptions

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

2 files changed, 29 insertions, 5 deletions

diff --git a/arch/arc/include/asm/arcregs.h b/arch/arc/include/asm/arcregs.h
index f1b86cef0905..a27eafdc8260 100644
--- a/arch/arc/include/asm/arcregs.h
+++ b/arch/arc/include/asm/arcregs.h
@@ -151,6 +151,14 @@ struct bcr_isa_arcv2 {
 #endif
 };
 
+struct bcr_uarch_build_arcv2 {
+#ifdef CONFIG_CPU_BIG_ENDIAN
+        unsigned int pad:8, prod:8, maj:8, min:8;
+#else
+        unsigned int min:8, maj:8, prod:8, pad:8;
+#endif
+};
+
 struct bcr_mpy {
 #ifdef CONFIG_CPU_BIG_ENDIAN
         unsigned int pad:8, x1616:8, dsp:4, cycles:2, type:2, ver:8;
diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
index 93d4d6639873..7b2340996cf8 100644
--- a/arch/arc/kernel/setup.c
+++ b/arch/arc/kernel/setup.c
@@ -199,13 +199,29 @@ static void read_arc_build_cfg_regs(void)
                 cpu->bpu.ret_stk = 4 << bpu.rse;
 
                 if (cpu->core.family >= 0x54) {
-                        unsigned int exec_ctrl;
 
-                        READ_BCR(AUX_EXEC_CTRL, exec_ctrl);
-                        cpu->extn.dual_enb = !(exec_ctrl & 1);
+                        struct bcr_uarch_build_arcv2 uarch;
 
-                        /* dual issue always present for this core */
-                        cpu->extn.dual = 1;
+                        /*
+                         * The first 0x54 core (uarch maj:min 0:1 or 0:2) was
+                         * dual issue only (HS4x). But next uarch rev (1:0)
+                         * allows it be configured for single issue (HS3x)
+                         * Ensure we fiddle with dual issue only on HS4x
+                         */
+                        READ_BCR(ARC_REG_MICRO_ARCH_BCR, uarch);
+
+                        if (uarch.prod == 4) {
+                                unsigned int exec_ctrl;
+
+                                /* dual issue hardware always present */
+                                cpu->extn.dual = 1;
+
+                                READ_BCR(AUX_EXEC_CTRL, exec_ctrl);
+
+                                /* dual issue hardware enabled ? */
+                                cpu->extn.dual_enb = !(exec_ctrl & 1);
+
+                        }
                 }
         }