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Date:      Wed, 7 Oct 2015 09:12:50 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r288983 - in head/sys/arm: arm include
Message-ID:  <201510070912.t979Co21054138@repo.freebsd.org>
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Author: kib
Date: Wed Oct  7 09:12:49 2015
New Revision: 288983
URL: https://svnweb.freebsd.org/changeset/base/288983

Log:
  A follow-up to r288492.  In fact, revert the mentioned commit for
  pre-VFPv3 processors, since they do require software support code to
  handle denormals.  For VFPv3 and later, enable flush-to-zero if
  hardware does not claim full denormals arithmetic support by VMVFR1_FZ
  field in mvfr1 register.
  
  The end result is that we do use correct fpu environment on Cortexes
  with VFPv3, while ARM11 (e.g. rpi) is in non-compliant flush-to-zero
  mode.  At least CPUs without complete hardware implementation of
  IEEE 754 do not cause unhandled floating point exception on underflow,
  as it was before r288492.
  
  Noted by:	ian
  Tested by:	gjb
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/arm/arm/vfp.c
  head/sys/arm/arm/vm_machdep.c
  head/sys/arm/include/md_var.h

Modified: head/sys/arm/arm/vfp.c
==============================================================================
--- head/sys/arm/arm/vfp.c	Wed Oct  7 08:56:38 2015	(r288982)
+++ head/sys/arm/arm/vfp.c	Wed Oct  7 09:12:49 2015	(r288983)
@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 #include <machine/armreg.h>
 #include <machine/frame.h>
 #include <machine/fp.h>
+#include <machine/md_var.h>
 #include <machine/pcb.h>
 #include <machine/undefined.h>
 #include <machine/vfp.h>
@@ -128,6 +129,15 @@ vfp_init(void)
 
 			tmp = fmrx(mvfr1);
 			PCPU_SET(vfpmvfr1, tmp);
+
+			if (PCPU_GET(cpuid) == 0) {
+				if ((tmp & VMVFR1_FZ_MASK) == 0x1) {
+					/* Denormals arithmetic support */
+					initial_fpscr &= ~VFPSCR_FZ;
+					thread0.td_pcb->pcb_vfpstate.fpscr =
+					    initial_fpscr;
+				}
+			}
 		}
 
 		/* initialize the coprocess 10 and 11 calls

Modified: head/sys/arm/arm/vm_machdep.c
==============================================================================
--- head/sys/arm/arm/vm_machdep.c	Wed Oct  7 08:56:38 2015	(r288982)
+++ head/sys/arm/arm/vm_machdep.c	Wed Oct  7 09:12:49 2015	(r288983)
@@ -85,6 +85,8 @@ __FBSDID("$FreeBSD$");
 CTASSERT(sizeof(struct switchframe) == 48);
 CTASSERT(sizeof(struct trapframe) == 80);
 
+uint32_t initial_fpscr = VFPSCR_DN | VFPSCR_FZ;
+
 /*
  * Finish a fork operation, with process p2 nearly set up.
  * Copy and update the pcb, set up the stack so that the child
@@ -134,7 +136,7 @@ cpu_fork(register struct thread *td1, re
 	pcb2->pcb_regs.sf_sp = STACKALIGN(td2->td_frame);
 
 	pcb2->pcb_vfpcpu = -1;
-	pcb2->pcb_vfpstate.fpscr = VFPSCR_DN;
+	pcb2->pcb_vfpstate.fpscr = initial_fpscr;
 
 	tf = td2->td_frame;
 	tf->tf_spsr &= ~PSR_C;

Modified: head/sys/arm/include/md_var.h
==============================================================================
--- head/sys/arm/include/md_var.h	Wed Oct  7 08:56:38 2015	(r288982)
+++ head/sys/arm/include/md_var.h	Wed Oct  7 09:12:49 2015	(r288983)
@@ -71,4 +71,6 @@ void dump_add_page(vm_paddr_t);
 void dump_drop_page(vm_paddr_t);
 int minidumpsys(struct dumperinfo *);
 
+extern uint32_t initial_fpscr;
+
 #endif /* !_MACHINE_MD_VAR_H_ */

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