Re: [PATCH v10 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

From: Jia He
Date: Wed Oct 09 2019 - 02:30:05 EST

Hi Suzuki

On 2019/10/8 23:32, Suzuki K Poulose wrote:

On 08/10/2019 02:12, Justin He (Arm Technology China) wrote:
Hi Will and Marc
Sorry for the late response, just came back from a vacation.

-----Original Message-----
From: Marc Zyngier <maz@xxxxxxxxxx>
Sent: 2019å10æ1æ 21:19
To: Will Deacon <will@xxxxxxxxxx>
Cc: Justin He (Arm Technology China) <Justin.He@xxxxxxx>; Catalin
Marinas <Catalin.Marinas@xxxxxxx>; Mark Rutland
<Mark.Rutland@xxxxxxx>; James Morse <James.Morse@xxxxxxx>;
Matthew Wilcox <willy@xxxxxxxxxxxxx>; Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; Punit Agrawal
<punitagrawal@xxxxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx>;
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; hejianet@xxxxxxxxx; Kaly
Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>
Subject: Re: [PATCH v10 1/3] arm64: cpufeature: introduce helper

On Tue, 1 Oct 2019 13:54:47 +0100
Will Deacon <will@xxxxxxxxxx> wrote:

On Mon, Sep 30, 2019 at 09:57:38AM +0800, Jia He wrote:
We unconditionally set the HW_AFDBM capability and only enable it on
CPUs which really have the feature. But sometimes we need to know
whether this cpu has the capability of HW AF. So decouple AF from
DBM by new helper cpu_has_hw_af().

Signed-off-by: Jia He <justin.he@xxxxxxx>
Suggested-by: Suzuki Poulose <Suzuki.Poulose@xxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
 arch/arm64/include/asm/cpufeature.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h
index 9cde5d2e768f..949bc7c85030 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -659,6 +659,16 @@ static inline u32
id_aa64mmfr0_parange_to_phys_shift(int parange)
ÂÂ default: return CONFIG_ARM64_PA_BITS;
ÂÂ }
+/* Check whether hardware update of the Access flag is supported */
+static inline bool cpu_has_hw_af(void)
+ÂÂÂÂÂÂÂÂ return read_cpuid(ID_AA64MMFR1_EL1) & 0xf;

0xf? I think we should have a mask in sysreg.h for this constant.

We don't have the mask, but we certainly have the shift.

of a mouthful though. Ideally, we'd have a helper for that.

Ok, I will implement the helper if there isn't so far.
And then replace the 0xf with it.

Or could we simpl reuse existing cpuid_feature_extract_unsigned_field() ?

u64 mmfr1 = read_cpuid(ID_AA64MMFR1_EL1);

return cpuid_feature_extract_unsigned_field(mmfr1, ID_AA64MMFR1_HADBS_SHIFT) ?

Yes, we can, I will send the new version

Justin (Jia He)