nios2: fix out of reach case for do_reset

The "Nios II Processor Reference Handbook" said,
"call can transfer execution anywhere within the 256 MByte range determined by PC31..28. The Nios II GNU linker does not automatically handle cases in which the address is out of this range."

So we have to use registered "callr" instruction to do the job.

Quoted 5 lines · Thomas Chou

The "Nios II Processor Reference Handbook" said,
"call can transfer execution anywhere within the 256 MByte range determined by PC31..28. The Nios II GNU linker does not automatically handle cases in which the address is out of this range."

Quoted 1 line

So we have to use registered "callr" instruction to do the job.

doesnt NIOS have an insn to call indirectly via a register ? typically that's how function pointers should be handled when gcc generates code.
-mike

The "Nios II Processor Reference Handbook" said,
"call can transfer execution anywhere within the 256 MByte range determined by PC31..28. The Nios II GNU linker does not automatically handle cases in which the address is out of this range."

So we have to use registered "callr" instruction to do the job.

Signed-off-by Thomas Chou <[email protected]>

---
 arch/nios2/cpu/cpu.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

arch/nios2/cpu/cpu.c +8 -6

index 6379534..d9c3003 100644
@@ -40,11 +40,13 @@ int checkcpu (void)
 	return (0);
 }
 
-
-int do_reset (void)
+int do_reset(void)
 {
-	void (*rst)(void) = (void(*)(void))CONFIG_SYS_RESET_ADDR;
-	disable_interrupts ();
-	rst();
-	return(0);
+	disable_interrupts();
+	__asm__ __volatile__ (
+	"callr	%0"
+	:
+	: "r" (CONFIG_SYS_RESET_ADDR)
+	);
+	return 0;
 }

As a comment, that patch looks pretty ugly. I might suggest an inline function (called "callr" or "nios2_callr") which
encapsulates the __asm__. That would make the code much easier to read.

You could put the inline function in one of the asm headers.

-brad

There is a limitation (or bug?) of nios2 toolchain. The nios2 gcc didn't generate correct code when the reset vector is passed as a constant. It just generated a direct "call", which was wrong when the reset vector was not located in the same 256MB span as u-boot.

The "Nios II Processor Reference Handbook" said,
"call can transfer execution anywhere within the 256 MByte range determined by PC31..28. The Nios II GNU linker does not automatically handle cases in which the address is out of this range."

So we have to use registered "callr" instruction to do the job.

Signed-off-by Thomas Chou <[email protected]>

---
v2, add a macro for the inlince asm nios2_callr.

 arch/nios2/cpu/cpu.c            |   11 +++++------
 arch/nios2/include/asm/system.h |    5 +++++
 2 files changed, 10 insertions(+), 6 deletions(-)

arch/nios2/cpu/cpu.c +5 -6

index 6379534..d9c6544 100644
@@ -40,11 +40,10 @@ int checkcpu (void)
 	return (0);
 }
 
-
-int do_reset (void)
+int do_reset(void)
 {
-	void (*rst)(void) = (void(*)(void))CONFIG_SYS_RESET_ADDR;
-	disable_interrupts ();
-	rst();
-	return(0);
+	disable_interrupts();
+	/* indirect call to go beyond 256MB limitation of toolchain */
+	nios2_callr(CONFIG_SYS_RESET_ADDR);
+	return 0;
 }

arch/nios2/include/asm/system.h +5 -0

index bb03ca5..086d92b 100644
@@ -56,4 +56,9 @@
 	((flags & NIOS2_STATUS_PIE_MSK) == 0x0);	\
 })
 
+/* indirect call to go beyond 256MB limitation of toolchain */
+#define nios2_callr(addr) __asm__ __volatile__ (	\
+	"callr	%0"					\
+	: : "r" (addr))
+
 #endif /* __ASM_NIOS2_SYSTEM_H */