After commit 846a136881b8f73c1f74250bf6acfaa309cab1f2 ("ARM: vfp: fix
saving d16-d31 vfp registers on v6+ kernels"), the OMAP 2430SDP board
started crashing during boot with omap2plus_defconfig:
[ 3.875122] mmcblk0: mmc0:e624 SD04G 3.69 GiB
[ 3.915954] mmcblk0: p1
[ 4.086639] Internal error: Oops - undefined instruction: 0 [#1] SMP ARM
[ 4.093719] Modules linked in:
[ 4.096954] CPU: 0 Not tainted (3.6.0-02232-g759e00b #570)
[ 4.103149] PC is at vfp_reload_hw+0x1c/0x44
[ 4.107666] LR is at __und_usr_fault_32+0x0/0x8
It turns out that the context save/restore fix unmasked a latent bug
in commit 5aaf254409f8d58229107b59507a8235b715a960 ("ARM: 6203/1: Make
VFPv3 usable on ARMv6"). When CONFIG_VFPv3 is set, but the kernel is
booted on a pre-VFPv3 core, the code attempts to save and restore the
d16-d31 VFP registers. These are only present on non-D16 VFPv3+, so
this results in an undefined instruction exception. The code didn't
crash before commit 846a136 because the save and restore code was
only touching d0-d15, present on all VFP.
Fix by implementing a request from Russell King to add a new HWCAP
flag that affirmatively indicates the presence of the d16-d31
registers:
http://marc.info/?l=linux-arm-kernel&m=135013547905283&w=2
and some feedback from Måns to clarify the name of the HWCAP flag.
Signed-off-by: Paul Walmsley <paul@xxxxxxxxx>
Cc: Tony Lindgren <tony@xxxxxxxxxxx>
Cc: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dave Martin <dave.martin@xxxxxxxxxx>
Cc: Måns Rullgård <mans.rullgard@xxxxxxxxxx>
---
Thanks for the suggestion, Måns; certainly a readability improvement.
arch/arm/include/asm/vfpmacros.h | 12 ++++++------
arch/arm/include/uapi/asm/hwcap.h | 3 ++-
arch/arm/vfp/vfpmodule.c | 9 ++++++---
3 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/arch/arm/include/asm/vfpmacros.h b/arch/arm/include/asm/vfpmacros.h
index 6a6f1e4..301c1db 100644
--- a/arch/arm/include/asm/vfpmacros.h
+++ b/arch/arm/include/asm/vfpmacros.h
@@ -27,9 +27,9 @@
#if __LINUX_ARM_ARCH__ <= 6
ldr \tmp, =elf_hwcap @ may not have MVFR regs
ldr \tmp, [\tmp, #0]
- tst \tmp, #HWCAP_VFPv3D16
- ldceql p11, cr0, [\base],#32*4 @ FLDMIAD \base!, {d16-d31}
- addne \base, \base, #32*4 @ step over unused register space
+ tst \tmp, #HWCAP_VFPD32
+ ldcnel p11, cr0, [\base],#32*4 @ FLDMIAD \base!, {d16-d31}
+ addeq \base, \base, #32*4 @ step over unused register space
#else
VFPFMRX \tmp, MVFR0 @ Media and VFP Feature Register 0
and \tmp, \tmp, #MVFR0_A_SIMD_MASK @ A_SIMD field
@@ -51,9 +51,9 @@
#if __LINUX_ARM_ARCH__ <= 6
ldr \tmp, =elf_hwcap @ may not have MVFR regs
ldr \tmp, [\tmp, #0]
- tst \tmp, #HWCAP_VFPv3D16
- stceql p11, cr0, [\base],#32*4 @ FSTMIAD \base!, {d16-d31}
- addne \base, \base, #32*4 @ step over unused register space
+ tst \tmp, #HWCAP_VFPD32
+ stcnel p11, cr0, [\base],#32*4 @ FSTMIAD \base!, {d16-d31}
+ addeq \base, \base, #32*4 @ step over unused register space
#else
VFPFMRX \tmp, MVFR0 @ Media and VFP Feature Register 0
and \tmp, \tmp, #MVFR0_A_SIMD_MASK @ A_SIMD field
diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h
index f254f65..3688fd1 100644
--- a/arch/arm/include/uapi/asm/hwcap.h
+++ b/arch/arm/include/uapi/asm/hwcap.h
@@ -18,11 +18,12 @@
#define HWCAP_THUMBEE (1 << 11)
#define HWCAP_NEON (1 << 12)
#define HWCAP_VFPv3 (1 << 13)
-#define HWCAP_VFPv3D16 (1 << 14)
+#define HWCAP_VFPv3D16 (1 << 14) /* also set for VFPv4-D16 */
#define HWCAP_TLS (1 << 15)
#define HWCAP_VFPv4 (1 << 16)
#define HWCAP_IDIVA (1 << 17)
#define HWCAP_IDIVT (1 << 18)
+#define HWCAP_VFPD32 (1 << 19) /* set if VFP has 32 regs (not 16) */
#define HWCAP_IDIV (HWCAP_IDIVA | HWCAP_IDIVT)
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index c834b32..3b44e0d 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -701,11 +701,14 @@ static int __init vfp_init(void)
elf_hwcap |= HWCAP_VFPv3;
/*
- * Check for VFPv3 D16. CPUs in this configuration
- * only have 16 x 64bit registers.
+ * Check for VFPv3 D16 and VFPv4 D16. CPUs in
+ * this configuration only have 16 x 64bit
+ * registers.
*/
if (((fmrx(MVFR0) & MVFR0_A_SIMD_MASK)) == 1)
- elf_hwcap |= HWCAP_VFPv3D16;
+ elf_hwcap |= HWCAP_VFPv3D16; /* also v4-D16 */
+ else
+ elf_hwcap |= HWCAP_VFPD32;
}
#endif
/*
--
1.7.10.4
