[PATCH v6] ARM: vfp: Always save VFP state in vfp_pm_suspend on UP

[PATCH v6] ARM: vfp: Always save VFP state in vfp_pm_suspend on UP

[Colin Cross]

vfp_pm_suspend should save the VFP state in suspend after
any lazy context switch.  If it only saves when the VFP is enabled,
the state can get lost when, on a UP system:
  Thread 1 uses the VFP
  Context switch occurs to thread 2, VFP is disabled but the
     VFP context is not saved
  Thread 2 initiates suspend
  vfp_pm_suspend is called with the VFP disabled, and the unsaved
     VFP context of Thread 1 in the registers

Modify vfp_pm_suspend to save the VFP context whenever
vfp_current_hw_state is not NULL.

Includes a fix from Ido Yariv <ido@wizery.com>, who pointed out that on
SMP systems, the state pointer can be pointing to a freed task struct if
a task exited on another cpu, fixed by using #ifdef CONFIG_SMP in the
new if clause.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Barry Song <bs14@csr.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ido Yariv <ido@wizery.com>
Cc: Daniel Drake <dsd@laptop.org>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Colin Cross <ccross@android.com>
---
 arch/arm/vfp/vfpmodule.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 58696192..ce55f05 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -457,6 +457,12 @@ static int vfp_pm_suspend(void)
 
 		/* disable, just in case */
 		fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
+	} else if (vfp_current_hw_state[ti->cpu]) {
+#ifndef CONFIG_SMP
+		fmxr(FPEXC, fpexc | FPEXC_EN);
+		vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
+		fmxr(FPEXC, fpexc);
+#endif
 	}
 
 	/* clear any information we had about last context state */
-- 
1.7.7.3

[PATCH v6] ARM: vfp: Always save VFP state in vfp_pm_suspend on UP

[Nicolas Pitre]

On Mon, 16 Jul 2012, Colin Cross wrote:

> vfp_pm_suspend should save the VFP state in suspend after
> any lazy context switch.  If it only saves when the VFP is enabled,
> the state can get lost when, on a UP system:
>   Thread 1 uses the VFP
>   Context switch occurs to thread 2, VFP is disabled but the
>      VFP context is not saved
>   Thread 2 initiates suspend
>   vfp_pm_suspend is called with the VFP disabled, and the unsaved
>      VFP context of Thread 1 in the registers
> 
> Modify vfp_pm_suspend to save the VFP context whenever
> vfp_current_hw_state is not NULL.
> 
> Includes a fix from Ido Yariv <ido@wizery.com>, who pointed out that on
> SMP systems, the state pointer can be pointing to a freed task struct if
> a task exited on another cpu, fixed by using #ifdef CONFIG_SMP in the
> new if clause.
> 
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Barry Song <bs14@csr.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Ido Yariv <ido@wizery.com>
> Cc: Daniel Drake <dsd@laptop.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Colin Cross <ccross@android.com>
> ---
>  arch/arm/vfp/vfpmodule.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
> index 58696192..ce55f05 100644
> --- a/arch/arm/vfp/vfpmodule.c
> +++ b/arch/arm/vfp/vfpmodule.c
> @@ -457,6 +457,12 @@ static int vfp_pm_suspend(void)
>  
>  		/* disable, just in case */
>  		fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
> +	} else if (vfp_current_hw_state[ti->cpu]) {
> +#ifndef CONFIG_SMP
> +		fmxr(FPEXC, fpexc | FPEXC_EN);
> +		vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
> +		fmxr(FPEXC, fpexc);
> +#endif
>  	}

Couldn't vfp_sync_hwstate() be used here instead?


Nicolas

[PATCH v6] ARM: vfp: Always save VFP state in vfp_pm_suspend on UP

[Colin Cross]

On Mon, Jul 16, 2012 at 11:34 AM, Nicolas Pitre
<nicolas.pitre@linaro.org> wrote:
> On Mon, 16 Jul 2012, Colin Cross wrote:
>
>> vfp_pm_suspend should save the VFP state in suspend after
>> any lazy context switch.  If it only saves when the VFP is enabled,
>> the state can get lost when, on a UP system:
>>   Thread 1 uses the VFP
>>   Context switch occurs to thread 2, VFP is disabled but the
>>      VFP context is not saved
>>   Thread 2 initiates suspend
>>   vfp_pm_suspend is called with the VFP disabled, and the unsaved
>>      VFP context of Thread 1 in the registers
>>
>> Modify vfp_pm_suspend to save the VFP context whenever
>> vfp_current_hw_state is not NULL.
>>
>> Includes a fix from Ido Yariv <ido@wizery.com>, who pointed out that on
>> SMP systems, the state pointer can be pointing to a freed task struct if
>> a task exited on another cpu, fixed by using #ifdef CONFIG_SMP in the
>> new if clause.
>>
>> Cc: Russell King <linux@arm.linux.org.uk>
>> Cc: Barry Song <bs14@csr.com>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Ido Yariv <ido@wizery.com>
>> Cc: Daniel Drake <dsd@laptop.org>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Signed-off-by: Colin Cross <ccross@android.com>
>> ---
>>  arch/arm/vfp/vfpmodule.c |    6 ++++++
>>  1 files changed, 6 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
>> index 58696192..ce55f05 100644
>> --- a/arch/arm/vfp/vfpmodule.c
>> +++ b/arch/arm/vfp/vfpmodule.c
>> @@ -457,6 +457,12 @@ static int vfp_pm_suspend(void)
>>
>>               /* disable, just in case */
>>               fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
>> +     } else if (vfp_current_hw_state[ti->cpu]) {
>> +#ifndef CONFIG_SMP
>> +             fmxr(FPEXC, fpexc | FPEXC_EN);
>> +             vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
>> +             fmxr(FPEXC, fpexc);
>> +#endif
>>       }
>
> Couldn't vfp_sync_hwstate() be used here instead?

Not easily, we don't have the thread struct of the thread that is in
the vfp hardware.  We would have to read vfp_current_hw_state for the
current cpu and use container_of to get from  struct vfpstate to
struct thread_info, and then pass that back in to vfp_sync_hwstate.