Re: [PATCH v3 2/2] xen/arm32: implement VFP context switch

[Julien Grall <julien.grall@linaro.org>]

On 06/03/2013 03:15 PM, Ian Campbell wrote:

> On Mon, 2013-06-03 at 15:00 +0100, Julien Grall wrote:
>> Add support for VFP context switch on arm32 and a dummy support for arm64
>>
>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>>
>> Changes in v3:
>>     - Add vfp_init to check if the processor supports VFP 3
>>     - Add clobber memory
>>     - Remove tmps
>>     - s/COFNIG_ARM64/CONFIG_ARM64/ in include/asm/arm.h
>>
>> Changes in v2:
>>     - Fix all the small errors (type, lost headers...)
>>     - Add some comments
>> ---
>>  xen/arch/arm/arm32/Makefile     |    1 +
>>  xen/arch/arm/arm32/vfp.c        |   99 +++++++++++++++++++++++++++++++++++++++
>>  xen/arch/arm/arm64/Makefile     |    1 +
>>  xen/arch/arm/arm64/vfp.c        |   13 +++++
>>  xen/arch/arm/domain.c           |    7 ++-
>>  xen/include/asm-arm/arm32/vfp.h |   41 ++++++++++++++++
>>  xen/include/asm-arm/arm64/vfp.h |   16 +++++++
>>  xen/include/asm-arm/cpregs.h    |    9 ++++
>>  xen/include/asm-arm/domain.h    |    4 ++
>>  xen/include/asm-arm/vfp.h       |   25 ++++++++++
>>  10 files changed, 214 insertions(+), 2 deletions(-)
>>  create mode 100644 xen/arch/arm/arm32/vfp.c
>>  create mode 100644 xen/arch/arm/arm64/vfp.c
>>  create mode 100644 xen/include/asm-arm/arm32/vfp.h
>>  create mode 100644 xen/include/asm-arm/arm64/vfp.h
>>  create mode 100644 xen/include/asm-arm/vfp.h
>>
>> diff --git a/xen/arch/arm/arm32/Makefile b/xen/arch/arm/arm32/Makefile
>> index aaf277a..b903803 100644
>> --- a/xen/arch/arm/arm32/Makefile
>> +++ b/xen/arch/arm/arm32/Makefile
>> @@ -6,5 +6,6 @@ obj-y += proc-ca15.o
>>  
>>  obj-y += traps.o
>>  obj-y += domain.o
>> +obj-y += vfp.o
>>  
>>  obj-$(EARLY_PRINTK) += debug.o
>> diff --git a/xen/arch/arm/arm32/vfp.c b/xen/arch/arm/arm32/vfp.c
>> new file mode 100644
>> index 0000000..2ece43d
>> --- /dev/null
>> +++ b/xen/arch/arm/arm32/vfp.c
>> @@ -0,0 +1,99 @@
>> +#include <xen/sched.h>
>> +#include <xen/init.h>
>> +#include <asm/processor.h>
>> +#include <asm/vfp.h>
>> +
>> +void vfp_save_state(struct vcpu *v)
>> +{
>> +    v->arch.vfp.fpexc = READ_CP32(FPEXC);
>> +
>> +    WRITE_CP32(v->arch.vfp.fpexc | FPEXC_EN, FPEXC);
>> +
>> +    v->arch.vfp.fpscr = READ_CP32(FPSCR);
>> +
>> +    if ( v->arch.vfp.fpexc & FPEXC_EX ) /* Check for sub-architecture */
>> +    {
>> +        v->arch.vfp.fpinst = READ_CP32(FPINST);
>> +
>> +        if ( v->arch.vfp.fpexc & FPEXC_FP2V )
>> +            v->arch.vfp.fpinst2 = READ_CP32(FPINST2);
>> +        /* Disable FPEXC_EX */
>> +        WRITE_CP32((v->arch.vfp.fpexc | FPEXC_EN) & ~FPEXC_EX, FPEXC);
>> +    }
>> +
>> +    /* Save {d0-d15} */
>> +    asm volatile("stc p11, cr0, [%0], #32*4"
>> +                 : : "r" (v->arch.vfp.fpregs1)
>> +                 : "memory");
> 
> http://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html suggests that
> "=m" (v->arch.vfp.fpregs1) or "=Q" (...) as output constraints might do
> the job without clobbering the whole of memory.

I'm not sure to fully understand the concept behind "=m". Does it mean
that gcc will clobber all the memory range addressed by fpregs?

-- 
Julien