[PATCH v5 3/6] bswap: Add the ability to store to an unaligned 24 bit field

[Jonathan Cameron via <qemu-devel@nongnu.org>]

From: Ira Weiny <ira.weiny@intel.com>

CXL has 24 bit unaligned fields which need to be stored to.  CXL is
specified as little endian.

Define st24_le_p() and the supporting functions to store such a field
from a 32 bit host native value.

The use of b, w, l, q as the size specifier is limiting.  So "24" was
used for the size part of the function name.

Reviewed-by: Fan Ni <fan.ni@samsung.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v5:
  - Added assertion that upper bits of the input parameter aren't set.
  - Mask value in bswap24s()
  - update docs
---
 docs/devel/loads-stores.rst |  1 +
 include/qemu/bswap.h        | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/docs/devel/loads-stores.rst b/docs/devel/loads-stores.rst
index ad5dfe133e..57b4396f7a 100644
--- a/docs/devel/loads-stores.rst
+++ b/docs/devel/loads-stores.rst
@@ -36,6 +36,7 @@ store: ``st{size}_{endian}_p(ptr, val)``
 ``size``
  - ``b`` : 8 bits
  - ``w`` : 16 bits
+ - ``24`` : 24 bits
  - ``l`` : 32 bits
  - ``q`` : 64 bits
 
diff --git a/include/qemu/bswap.h b/include/qemu/bswap.h
index 15a78c0db5..91ed9c7e2c 100644
--- a/include/qemu/bswap.h
+++ b/include/qemu/bswap.h
@@ -8,11 +8,25 @@
 #undef  bswap64
 #define bswap64(_x) __builtin_bswap64(_x)
 
+static inline uint32_t bswap24(uint32_t x)
+{
+    assert((x & 0xff000000U) == 0);
+
+    return (((x & 0x000000ffU) << 16) |
+            ((x & 0x0000ff00U) <<  0) |
+            ((x & 0x00ff0000U) >> 16));
+}
+
 static inline void bswap16s(uint16_t *s)
 {
     *s = __builtin_bswap16(*s);
 }
 
+static inline void bswap24s(uint32_t *s)
+{
+    *s = bswap24(*s & 0x00ffffffU);
+}
+
 static inline void bswap32s(uint32_t *s)
 {
     *s = __builtin_bswap32(*s);
@@ -176,6 +190,7 @@ CPU_CONVERT(le, 64, uint64_t)
  * size is:
  *   b: 8 bits
  *   w: 16 bits
+ *   24: 24 bits
  *   l: 32 bits
  *   q: 64 bits
  *
@@ -248,6 +263,11 @@ static inline void stw_he_p(void *ptr, uint16_t v)
     __builtin_memcpy(ptr, &v, sizeof(v));
 }
 
+static inline void st24_he_p(void *ptr, uint32_t v)
+{
+    __builtin_memcpy(ptr, &v, 3);
+}
+
 static inline int ldl_he_p(const void *ptr)
 {
     int32_t r;
@@ -297,6 +317,11 @@ static inline void stw_le_p(void *ptr, uint16_t v)
     stw_he_p(ptr, le_bswap(v, 16));
 }
 
+static inline void st24_le_p(void *ptr, uint32_t v)
+{
+    st24_he_p(ptr, le_bswap(v, 24));
+}
+
 static inline void stl_le_p(void *ptr, uint32_t v)
 {
     stl_he_p(ptr, le_bswap(v, 32));
-- 
2.37.2