Fixes for secondary CPU start-up.

Changes to make secondary CPU start-up work on NetBSD, which depends
on some specific behavior in the architecture specification:

- Change the internal swppal() function to take the new VPTPTR and
  Procedure Value as explicit arguments.  Adapt do_start() to the
  new the new swppal() signature.

- In do_start_wait(), extract the new VPTPTR and PV from the relevant
  HWRPB fields, which will have been initialized by the OS, and pass
  them to swppal().

- In the SWPPAL PAL call, get the value to stuff into PV (r27) from
  a4 (r20), and add a comment describing why this implementation detail
  is allowed by the architecture specification.

Signed-off-by: Jason Thorpe <thorpej@me.com>
Message-Id: <20210603035317.6814-9-thorpej@me.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

2 files changed, 25 insertions, 13 deletions

diff --git a/init.c b/init.c
index 1451785..6edfdf2 100644
--- a/init.c
+++ b/init.c
@@ -288,14 +288,16 @@ init_i8259 (void)
 }
 
 static void __attribute__((noreturn))
-swppal(void *entry, void *pcb)
+swppal(void *entry, void *pcb, unsigned long vptptr, unsigned long pv)
 {
   register int variant __asm__("$16") = 2;	/* OSF/1 PALcode */
   register void *pc __asm__("$17") = entry;
   register unsigned long pa_pcb __asm__("$18") = PA(pcb);
-  register unsigned long vptptr __asm__("$19") = VPTPTR;
+  register unsigned long newvptptr __asm__("$19") = vptptr;
+  register unsigned long newpv __asm__("$20") = pv;
 
-  asm("call_pal 0x0a" : : "r"(variant), "r"(pc), "r"(pa_pcb), "r"(vptptr));
+  asm("call_pal 0x0a" : :
+      "r"(variant), "r"(pc), "r"(pa_pcb), "r"(newvptptr), "r"(newpv));
   __builtin_unreachable ();
 }
 
@@ -313,7 +315,9 @@ do_start(unsigned long memsize, void (*kernel_entry)(void), unsigned long cpus)
   pci_setup();
   vgahw_init();
 
-  swppal(kernel_entry ? kernel_entry : do_console, &pcb);
+  void *new_pc = kernel_entry ? kernel_entry : do_console;
+
+  swppal(new_pc, &pcb, VPTPTR, (unsigned long)new_pc);
 }
 
 void
@@ -328,14 +332,16 @@ do_start_wait(unsigned long cpuid)
 	{
 	  /* ??? The only message I know of is "START\r\n".
 	     I can't be bothered to verify more than 4 characters.  */
-	  /* ??? The Linux kernel fills in, but does not require,
-	     CPU_restart_data.  It just sets that to the same address
-	     as CPU_restart itself.  Our swppal *does* put the PC into
-	     $26 and $27, the latter of which the kernel does rely upon.  */
+
+	  /* Use use a private extension to SWPPAL to get the
+	     CPU_restart_data into $27.  Linux fills it in, but does
+	     not require it. Other operating systems, however, do use
+	     CPU_restart_data as part of secondary CPU start-up.  */
 
 	  unsigned int len = hwrpb.processor[cpuid].ipc_buffer[0];
 	  unsigned int msg = hwrpb.processor[cpuid].ipc_buffer[1];
 	  void *CPU_restart = hwrpb.hwrpb.CPU_restart;
+	  unsigned long CPU_restart_data = hwrpb.hwrpb.CPU_restart_data;
 	  __sync_synchronize();
 	  hwrpb.hwrpb.rxrdy = 0;
 
@@ -343,7 +349,8 @@ do_start_wait(unsigned long cpuid)
 	    {
 	      /* Set bootstrap in progress */
 	      hwrpb.processor[cpuid].flags |= 1;
-	      swppal(CPU_restart, hwrpb.processor[cpuid].hwpcb);
+	      swppal(CPU_restart, hwrpb.processor[cpuid].hwpcb,
+		     hwrpb.hwrpb.vptb, CPU_restart_data);
 	    }
 	}
     }
diff --git a/pal.S b/pal.S
index 015a829..8d55a0a 100644
--- a/pal.S
+++ b/pal.S
@@ -566,6 +566,8 @@ ENDFN	CallPal_Cserve_Cont
  *	r17 (a1) = New PC
  *	r18 (a2) = New PCB
  *	r19 (a3) = New VptPtr
+ *	r20 (a4) = New Procedure Value (to place into $27)
+ *	           (Non-standard; See note below.)
  * 
  * OUTPUT PARAMETERS:
  *
@@ -574,11 +576,14 @@ ENDFN	CallPal_Cserve_Cont
  *			1 - Unknown PALcode variant
  *			2 - Known PALcode variant, but PALcode not loaded
  *
- *	r26 (ra) = r27 (pv) = New PC
+ *	r26 (ra) = New PC
+ *	r27 (pv) = From r20
  *		Note that this is non-architected, but is relied on by
  *		the usage of SwpPal within our own console code in order
- *		to simplify its use within C code.
- *
+ *		to simplify its use within C code.  We can get away with
+ *		the extra non-standard argument (in $20) because as
+ *		architected, all registers except SP and R0 are
+ *		UNPREDICTABLE; therefore private internal usage is fine.
  */
 	ORG_CALL_PAL_PRIV(0x0A)
 CallPal_SwpPal:
@@ -624,7 +629,7 @@ CallPal_SwpPal_Cont:
 	mtpr	$31, qemu_tbia		// Flush TLB for new PTBR
 
 	mov	a1, $26
-	mov	a1, $27
+	mov	a4, $27
 	hw_ret	(a1)
 ENDFN	CallPal_SwpPal_Cont
 	.previous