[Xen-changelog] [xen staging] xen/arm: cpufeature: Add helper to check constant caps

[patchbot@xxxxxxx]

commit 579401fb8e5f33dda461d872bf5a711072662d59
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Mon Oct 1 13:46:37 2018 +0100
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Mon Oct 1 13:45:15 2018 -0700

    xen/arm: cpufeature: Add helper to check constant caps
    
    Some capababilities are set right during boot and will never change
    afterwards. At the moment, the function cpu_have_caps will check whether
    the cap is enabled from the memory.
    
    It is possible to avoid the load from the memory by using an
    ALTERNATIVE. With that the check is just reduced to 1 instruction.
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/include/asm-arm/cpufeature.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
index 3de6b54301..c6cbc2ec84 100644
--- a/xen/include/asm-arm/cpufeature.h
+++ b/xen/include/asm-arm/cpufeature.h
@@ -63,6 +63,18 @@ static inline bool cpus_have_cap(unsigned int num)
     return test_bit(num, cpu_hwcaps);
 }
 
+/* System capability check for constant cap */
+#define cpus_have_const_cap(num) ({                 \
+        bool __ret;                                 \
+                                                    \
+        asm volatile (ALTERNATIVE("mov %0, #0",     \
+                                  "mov %0, #1",     \
+                                  num)              \
+                      : "=r" (__ret));              \
+                                                    \
+        unlikely(__ret);                            \
+        })
+
 static inline void cpus_set_cap(unsigned int num)
 {
     if (num >= ARM_NCAPS)
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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