Patchwork [v3,6/7] arm64: Advertise ARM64_HAS_DCPODP cpu feature

login
register
mail settings
Submitter Andrew Murray
Date April 1, 2019, 10:45 a.m.
Message ID <20190401104515.39775-7-andrew.murray@arm.com>
Download mbox | patch
Permalink /patch/32120/
State New
Headers show

Comments

Andrew Murray - April 1, 2019, 10:45 a.m.
Advertise ARM64_HAS_DCPOP when both DC CVAP and DC CVADP are supported.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
---
 arch/arm64/include/asm/cpucaps.h | 3 ++-
 arch/arm64/kernel/cpufeature.c   | 9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)
Dave Martin - April 2, 2019, 2:59 p.m.
On Mon, Apr 01, 2019 at 11:45:14AM +0100, Andrew Murray wrote:
> Advertise ARM64_HAS_DCPOP when both DC CVAP and DC CVADP are supported.

Do you mean ARM64_HAS_DCPODP?

And do we need this?  This capability flag doesn't currently appear to
be used for anything (which makes me wonder whether it _should_ be wired
up to something in the kernel).

Do we expect the kernel to do something special with this in the future?

OTOH, we get a nice printk when the feature is detected, and the code
size cost is insignificant.  So, if there's a reasonable expectation that
we will use it someday, I don't see a big problem with having it.

Cheers
---Dave

> 
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
>  arch/arm64/include/asm/cpucaps.h | 3 ++-
>  arch/arm64/kernel/cpufeature.c   | 9 +++++++++
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> index f6a76e43f39e..defdc67d9ab4 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -61,7 +61,8 @@
>  #define ARM64_HAS_GENERIC_AUTH_ARCH		40
>  #define ARM64_HAS_GENERIC_AUTH_IMP_DEF		41
>  #define ARM64_HAS_IRQ_PRIO_MASKING		42
> +#define ARM64_HAS_DCPODP			43
>  
> -#define ARM64_NCAPS				43
> +#define ARM64_NCAPS				44
>  
>  #endif /* __ASM_CPUCAPS_H */
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 5e27d2dbe45e..c74b25895c43 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1339,6 +1339,15 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>  		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
>  		.min_field_value = 1,
>  	},
> +	{
> +		.desc = "Data cache clean to Point of Deep Persistence",
> +		.capability = ARM64_HAS_DCPODP,
> +		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> +		.matches = has_cpuid_feature,
> +		.sys_reg = SYS_ID_AA64ISAR1_EL1,
> +		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
> +		.min_field_value = 2,
> +	},
>  #endif
>  #ifdef CONFIG_ARM64_SVE
>  	{
> -- 
> 2.21.0
>
Andrew Murray - April 3, 2019, 9:23 a.m.
On Tue, Apr 02, 2019 at 03:59:58PM +0100, Dave Martin wrote:
> On Mon, Apr 01, 2019 at 11:45:14AM +0100, Andrew Murray wrote:
> > Advertise ARM64_HAS_DCPOP when both DC CVAP and DC CVADP are supported.
> 
> Do you mean ARM64_HAS_DCPODP?

Yes I did - good catch.

> 
> And do we need this?  This capability flag doesn't currently appear to
> be used for anything (which makes me wonder whether it _should_ be wired
> up to something in the kernel).
> 
> Do we expect the kernel to do something special with this in the future?
> 
> OTOH, we get a nice printk when the feature is detected, and the code
> size cost is insignificant.  So, if there's a reasonable expectation that
> we will use it someday, I don't see a big problem with having it.

Yes it's not currently used, so I'm happy to drop this patch if people prefer
that - however it does complement the existing DCPOP cap which is present.

Thanks,

Andrew Murray

> 
> Cheers
> ---Dave
> 
> > 
> > Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> > ---
> >  arch/arm64/include/asm/cpucaps.h | 3 ++-
> >  arch/arm64/kernel/cpufeature.c   | 9 +++++++++
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> > index f6a76e43f39e..defdc67d9ab4 100644
> > --- a/arch/arm64/include/asm/cpucaps.h
> > +++ b/arch/arm64/include/asm/cpucaps.h
> > @@ -61,7 +61,8 @@
> >  #define ARM64_HAS_GENERIC_AUTH_ARCH		40
> >  #define ARM64_HAS_GENERIC_AUTH_IMP_DEF		41
> >  #define ARM64_HAS_IRQ_PRIO_MASKING		42
> > +#define ARM64_HAS_DCPODP			43
> >  
> > -#define ARM64_NCAPS				43
> > +#define ARM64_NCAPS				44
> >  
> >  #endif /* __ASM_CPUCAPS_H */
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 5e27d2dbe45e..c74b25895c43 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -1339,6 +1339,15 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> >  		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
> >  		.min_field_value = 1,
> >  	},
> > +	{
> > +		.desc = "Data cache clean to Point of Deep Persistence",
> > +		.capability = ARM64_HAS_DCPODP,
> > +		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> > +		.matches = has_cpuid_feature,
> > +		.sys_reg = SYS_ID_AA64ISAR1_EL1,
> > +		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
> > +		.min_field_value = 2,
> > +	},
> >  #endif
> >  #ifdef CONFIG_ARM64_SVE
> >  	{
> > -- 
> > 2.21.0
> >
Dave Martin - April 3, 2019, 9:32 a.m.
On Wed, Apr 03, 2019 at 10:23:42AM +0100, Andrew Murray wrote:
> On Tue, Apr 02, 2019 at 03:59:58PM +0100, Dave Martin wrote:
> > On Mon, Apr 01, 2019 at 11:45:14AM +0100, Andrew Murray wrote:
> > > Advertise ARM64_HAS_DCPOP when both DC CVAP and DC CVADP are supported.
> > 
> > Do you mean ARM64_HAS_DCPODP?
> 
> Yes I did - good catch.
> 
> > 
> > And do we need this?  This capability flag doesn't currently appear to
> > be used for anything (which makes me wonder whether it _should_ be wired
> > up to something in the kernel).
> > 
> > Do we expect the kernel to do something special with this in the future?
> > 
> > OTOH, we get a nice printk when the feature is detected, and the code
> > size cost is insignificant.  So, if there's a reasonable expectation that
> > we will use it someday, I don't see a big problem with having it.
> 
> Yes it's not currently used, so I'm happy to drop this patch if people prefer
> that - however it does complement the existing DCPOP cap which is present.

OK, sounds fine.

Maybe add a note in the commit message that this is here for consistency
with DCPOP, and we anticipate it being used in the future.

Cheers
---Dave
Andrew Murray - April 3, 2019, 9:57 a.m.
On Wed, Apr 03, 2019 at 10:32:43AM +0100, Dave Martin wrote:
> On Wed, Apr 03, 2019 at 10:23:42AM +0100, Andrew Murray wrote:
> > On Tue, Apr 02, 2019 at 03:59:58PM +0100, Dave Martin wrote:
> > > On Mon, Apr 01, 2019 at 11:45:14AM +0100, Andrew Murray wrote:
> > > > Advertise ARM64_HAS_DCPOP when both DC CVAP and DC CVADP are supported.
> > > 
> > > Do you mean ARM64_HAS_DCPODP?
> > 
> > Yes I did - good catch.
> > 
> > > 
> > > And do we need this?  This capability flag doesn't currently appear to
> > > be used for anything (which makes me wonder whether it _should_ be wired
> > > up to something in the kernel).
> > > 
> > > Do we expect the kernel to do something special with this in the future?
> > > 
> > > OTOH, we get a nice printk when the feature is detected, and the code
> > > size cost is insignificant.  So, if there's a reasonable expectation that
> > > we will use it someday, I don't see a big problem with having it.
> > 
> > Yes it's not currently used, so I'm happy to drop this patch if people prefer
> > that - however it does complement the existing DCPOP cap which is present.
> 
> OK, sounds fine.
> 
> Maybe add a note in the commit message that this is here for consistency
> with DCPOP, and we anticipate it being used in the future.

OK thanks,

Andrew Murray

> 
> Cheers
> ---Dave

Patch

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index f6a76e43f39e..defdc67d9ab4 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -61,7 +61,8 @@ 
 #define ARM64_HAS_GENERIC_AUTH_ARCH		40
 #define ARM64_HAS_GENERIC_AUTH_IMP_DEF		41
 #define ARM64_HAS_IRQ_PRIO_MASKING		42
+#define ARM64_HAS_DCPODP			43
 
-#define ARM64_NCAPS				43
+#define ARM64_NCAPS				44
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 5e27d2dbe45e..c74b25895c43 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1339,6 +1339,15 @@  static const struct arm64_cpu_capabilities arm64_features[] = {
 		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
 		.min_field_value = 1,
 	},
+	{
+		.desc = "Data cache clean to Point of Deep Persistence",
+		.capability = ARM64_HAS_DCPODP,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_cpuid_feature,
+		.sys_reg = SYS_ID_AA64ISAR1_EL1,
+		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
+		.min_field_value = 2,
+	},
 #endif
 #ifdef CONFIG_ARM64_SVE
 	{