* [PATCH] bitfield: add constant field preparation macros
@ 2018-10-12 19:45 Johannes Berg
2018-10-15 8:53 ` John Garry
0 siblings, 1 reply; 3+ messages in thread
From: Johannes Berg @ 2018-10-12 19:45 UTC (permalink / raw)
To: linux-wireless; +Cc: linux-kernel, John Garry, nbd, Johannes Berg
From: Johannes Berg <johannes.berg@intel.com>
John Garry requested to be able to use FIELD_PREP() and friends
in constant initializers, but we cannot completely switch all of
the current assertions to BUILD_BUG_ON_ZERO().
So instead of this, add __FIELD_PREP() which is suitable in such
contexts, and also add __{u,le,be}{16,32,64}encode_bits() like
the existing versions without underscores, but again suitable in
constant contexts.
Requested-by: John Garry <john.garry@huawei.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
include/linux/bitfield.h | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 3f1ef4450a7c..245dfb47d201 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -63,6 +63,14 @@
(1ULL << __bf_shf(_mask))); \
})
+#define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
+
+#define __BF_FIELD_CHECK_CONST(_mask, _reg, _val) \
+ (BUILD_BUG_ON_ZERO((_mask) == 0) + \
+ BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
+ BUILD_BUG_ON_ZERO((_mask) > (typeof(_reg))~0ull) + \
+ __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))))
+
/**
* FIELD_FIT() - check if value fits in the field
* @_mask: shifted mask defining the field's length and position
@@ -90,6 +98,21 @@
((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
})
+/**
+ * __FIELD_PREP() - prepare a constant bitfield element
+ * @_mask: shifted mask defining the field's length and position
+ * @_val: value to put in the field
+ *
+ * __FIELD_PREP() masks and shifts up the value. The result should
+ * be combined with other fields of the bitfield using local OR.
+ *
+ * This version is suitable for use in a pure constant context, e.g.
+ * a constant initializer.
+ */
+#define __FIELD_PREP(_mask, _val) \
+ ((typeof(_mask))__BF_FIELD_CHECK_CONST(_mask, 0ULL, _val) + \
+ (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask)))
+
/**
* FIELD_GET() - extract a bitfield element
* @_mask: shifted mask defining the field's length and position
@@ -150,4 +173,15 @@ __MAKE_OP(64)
#undef __MAKE_OP
#undef ____MAKE_OP
+#define __encode_bits(w, v, field) __FIELD_PREP((u##w)(field), v)
+#define __u16_encode_bits(v, field) __encode_bits(16, v, field)
+#define __le16_encode_bits(v, field) cpu_to_le16(__encode_bits(16, v, field))
+#define __be16_encode_bits(v, field) cpu_to_be16(__encode_bits(16, v, field))
+#define __u32_encode_bits(v, field) __encode_bits(32, v, field)
+#define __le32_encode_bits(v, field) cpu_to_le32(__encode_bits(32, v, field))
+#define __be32_encode_bits(v, field) cpu_to_be32(__encode_bits(32, v, field))
+#define __u64_encode_bits(v, field) __encode_bits(64, v, field)
+#define __le64_encode_bits(v, field) cpu_to_le64(__encode_bits(64, v, field))
+#define __be64_encode_bits(v, field) cpu_to_be64(__encode_bits(64, v, field))
+
#endif
--
2.17.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] bitfield: add constant field preparation macros
2018-10-12 19:45 [PATCH] bitfield: add constant field preparation macros Johannes Berg
@ 2018-10-15 8:53 ` John Garry
2018-10-15 14:54 ` Johannes Berg
0 siblings, 1 reply; 3+ messages in thread
From: John Garry @ 2018-10-15 8:53 UTC (permalink / raw)
To: Johannes Berg, linux-wireless; +Cc: linux-kernel, nbd, Johannes Berg
On 12/10/2018 20:45, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
>
> John Garry requested to be able to use FIELD_PREP() and friends
> in constant initializers, but we cannot completely switch all of
> the current assertions to BUILD_BUG_ON_ZERO().
>
Thanks for this.
> So instead of this, add __FIELD_PREP() which is suitable in such
> contexts, and also add __{u,le,be}{16,32,64}encode_bits() like
> the existing versions without underscores, but again suitable in
> constant contexts.
>
> Requested-by: John Garry <john.garry@huawei.com>
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> ---
> include/linux/bitfield.h | 34 ++++++++++++++++++++++++++++++++++
> 1 file changed, 34 insertions(+)
>
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 3f1ef4450a7c..245dfb47d201 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -63,6 +63,14 @@
> (1ULL << __bf_shf(_mask))); \
> })
>
> +#define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
> +
> +#define __BF_FIELD_CHECK_CONST(_mask, _reg, _val) \
> + (BUILD_BUG_ON_ZERO((_mask) == 0) + \
> + BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
> + BUILD_BUG_ON_ZERO((_mask) > (typeof(_reg))~0ull) + \
> + __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))))
> +
> /**
> * FIELD_FIT() - check if value fits in the field
> * @_mask: shifted mask defining the field's length and position
> @@ -90,6 +98,21 @@
> ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
> })
>
> +/**
> + * __FIELD_PREP() - prepare a constant bitfield element
My impression is that the name prefix - '__' - tells little about the
function. If you agree, how about even CFIELD_PREP() or
FIELD_PREP_CONST() or similar? I preper the latter, but becomes rather long.
> + * @_mask: shifted mask defining the field's length and position
> + * @_val: value to put in the field
> + *
> + * __FIELD_PREP() masks and shifts up the value. The result should
> + * be combined with other fields of the bitfield using local OR.
should this be 'logical OR', or indeed 'bitwise OR'?
> + *
> + * This version is suitable for use in a pure constant context, e.g.
> + * a constant initializer.
> + */
> +#define __FIELD_PREP(_mask, _val) \
> + ((typeof(_mask))__BF_FIELD_CHECK_CONST(_mask, 0ULL, _val) + \
> + (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask)))
> +
> /**
> * FIELD_GET() - extract a bitfield element
> * @_mask: shifted mask defining the field's length and position
> @@ -150,4 +173,15 @@ __MAKE_OP(64)
> #undef __MAKE_OP
> #undef ____MAKE_OP
>
> +#define __encode_bits(w, v, field) __FIELD_PREP((u##w)(field), v)
> +#define __u16_encode_bits(v, field) __encode_bits(16, v, field)
> +#define __le16_encode_bits(v, field) cpu_to_le16(__encode_bits(16, v, field))
> +#define __be16_encode_bits(v, field) cpu_to_be16(__encode_bits(16, v, field))
> +#define __u32_encode_bits(v, field) __encode_bits(32, v, field)
> +#define __le32_encode_bits(v, field) cpu_to_le32(__encode_bits(32, v, field))
> +#define __be32_encode_bits(v, field) cpu_to_be32(__encode_bits(32, v, field))
> +#define __u64_encode_bits(v, field) __encode_bits(64, v, field)
> +#define __le64_encode_bits(v, field) cpu_to_le64(__encode_bits(64, v, field))
> +#define __be64_encode_bits(v, field) cpu_to_be64(__encode_bits(64, v, field))
> +
> #endif
>
Thanks again,
John
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] bitfield: add constant field preparation macros
2018-10-15 8:53 ` John Garry
@ 2018-10-15 14:54 ` Johannes Berg
0 siblings, 0 replies; 3+ messages in thread
From: Johannes Berg @ 2018-10-15 14:54 UTC (permalink / raw)
To: John Garry, linux-wireless; +Cc: linux-kernel, nbd
On Mon, 2018-10-15 at 09:53 +0100, John Garry wrote:
> > +/**
> > + * __FIELD_PREP() - prepare a constant bitfield element
>
> My impression is that the name prefix - '__' - tells little about the
> function. If you agree, how about even CFIELD_PREP() or
> FIELD_PREP_CONST() or similar? I preper the latter, but becomes rather long.
I was following the __cpu_to_{be,le}{16,32,64} playbook, but don't
really care much. I'd prefer FIELD_PREP_CONST() over CFIELD_PREP()
though, so we can change this.
> > + * @_mask: shifted mask defining the field's length and position
> > + * @_val: value to put in the field
> > + *
> > + * __FIELD_PREP() masks and shifts up the value. The result should
> > + * be combined with other fields of the bitfield using local OR.
>
> should this be 'logical OR', or indeed 'bitwise OR'?
I'm not sure what happened there ... I copy/pasted the comment from
FIELD_PREP() but that says "logical OR" (which is in fact wrong, yes, it
should be say "bitwise OR").
johannes
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