Problem with 64-bit registers on i.MX53

[Russell King - ARM Linux]

On Mon, Oct 08, 2012 at 06:01:24PM +0100, Russell King - ARM Linux wrote:
> On Mon, Oct 08, 2012 at 06:08:41PM +0200, Michael Olbrich wrote:
> > 
> > Hi,
> > 
> > I have a problem that looks like that 64-bit registers (I think) are not
> > saved/restored correctly on a context switch. I've reduced it to the
> > following test case:
> > 
> > - Latest Linux mainline kernel (v3.6-8559-ge9eca4d)
> >   v3.5 is also affected
> > - imx_v6_v7_defconfig
> > - arch/arm/boot/dts/imx53-evk.dts
> > 
> > The following test program is compiled with "-mcpu=cortex-a8 -mfpu=neon
> > -O2".
> > ------------------------>8--------------------------------
> > #include <inttypes.h>
> > #include <assert.h>
> > 
> > volatile int x = 2;
> > volatile int64_t y = 2;
> > 
> > int main() {
> > 	volatile int a = 0;
> > 	volatile int64_t b = 0;
> > 	while (1) {
> > 		a = (a + x) % (1 << 30);
> > 		b = (b + y) % (1 << 30);
> > 		assert(a == b);
> > 	}
> > }
> > ------------------------>8--------------------------------
> > The ".. (b + y) .." should result in "vadd.i64 d19, d18, d16" or
> > something like that.
> 
> Hmm.
> 
> Can you send me the output of 'grep ^Features /proc/cpuinfo' please?

You may also like to try the patch below... it will probably fix your
problem.

diff --git a/arch/arm/include/asm/vfpmacros.h b/arch/arm/include/asm/vfpmacros.h
index a7aadbd..6a6f1e4 100644
--- a/arch/arm/include/asm/vfpmacros.h
+++ b/arch/arm/include/asm/vfpmacros.h
@@ -28,7 +28,7 @@
 	ldr	\tmp, =elf_hwcap		    @ may not have MVFR regs
 	ldr	\tmp, [\tmp, #0]
 	tst	\tmp, #HWCAP_VFPv3D16
-	ldceq	p11, cr0, [\base],#32*4		    @ FLDMIAD \base!, {d16-d31}
+	ldceql	p11, cr0, [\base],#32*4		    @ FLDMIAD \base!, {d16-d31}
 	addne	\base, \base, #32*4		    @ step over unused register space
 #else
 	VFPFMRX	\tmp, MVFR0			    @ Media and VFP Feature Register 0
@@ -52,7 +52,7 @@
 	ldr	\tmp, =elf_hwcap		    @ may not have MVFR regs
 	ldr	\tmp, [\tmp, #0]
 	tst	\tmp, #HWCAP_VFPv3D16
-	stceq	p11, cr0, [\base],#32*4		    @ FSTMIAD \base!, {d16-d31}
+	stceql	p11, cr0, [\base],#32*4		    @ FSTMIAD \base!, {d16-d31}
 	addne	\base, \base, #32*4		    @ step over unused register space
 #else
 	VFPFMRX	\tmp, MVFR0			    @ Media and VFP Feature Register 0