[PATCH rdma-next 04/23] net/mlx5: Add macros for reading log-based caps

[Yishai Hadas <yishaih@nvidia.com>]

From: Dragos Tatulea <dtatulea@nvidia.com>

Add macros that can be used to exponentiate log based capabilities.

When a capability can represent more than the used version (u32 , u64),
value will be clamped to the largest representable power of two.

Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
---
 include/linux/mlx5/device.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/include/linux/mlx5/device.h b/include/linux/mlx5/device.h
index 37727b5ab78f..f45454f65d5c 100644
--- a/include/linux/mlx5/device.h
+++ b/include/linux/mlx5/device.h
@@ -38,6 +38,7 @@
 #include <linux/mlx5/mlx5_ifc.h>
 #include <linux/mlx5/mlx5_ifc_macros.h>
 #include <linux/bitfield.h>
+#include <linux/minmax.h>
 
 #if defined(__LITTLE_ENDIAN)
 #define MLX5_SET_HOST_ENDIANNESS	0
@@ -47,6 +48,16 @@
 #error Host endianness not defined
 #endif
 
+/* Largest shift count that is defined behaviour for a value of type @T. */
+#define __mlx5_max_shift(T) (BITS_PER_TYPE(T) - 1 - is_signed_type(T))
+
+/* Calculate 2^@fld from a log2 cap field. Exponents that don't fit in @T
+ * saturate to the largest representable power of two (not to the type
+ * maximum), avoiding undefined shifts.
+ */
+#define MLX5_GET_LOGSZ_CLAMP(typ, p, fld, T) \
+	((T)((T)1 << min_t(u32, MLX5_GET(typ, p, fld), __mlx5_max_shift(T))))
+
 enum mlx5_inline_modes {
 	MLX5_INLINE_MODE_NONE,
 	MLX5_INLINE_MODE_L2,
@@ -1096,6 +1107,15 @@ enum mlx5_qcam_feature_groups {
 #define MLX5_CAP_GEN_MAX(mdev, cap) \
 	MLX5_GET(cmd_hca_cap, mdev->caps.hca[MLX5_CAP_GENERAL]->max, cap)
 
+/* 2^cap for log2-encoded general caps */
+#define MLX5_CAP_GEN_LOGSZ_U32(mdev, cap) \
+	MLX5_GET_LOGSZ_CLAMP(cmd_hca_cap, \
+			     mdev->caps.hca[MLX5_CAP_GENERAL]->cur, cap, u32)
+
+#define MLX5_CAP_GEN_LOGSZ_U64(mdev, cap) \
+	MLX5_GET_LOGSZ_CLAMP(cmd_hca_cap, \
+			     mdev->caps.hca[MLX5_CAP_GENERAL]->cur, cap, u64)
+
 #define MLX5_CAP_GEN_2(mdev, cap) \
 	MLX5_GET(cmd_hca_cap_2, mdev->caps.hca[MLX5_CAP_GENERAL_2]->cur, cap)
 
-- 
2.18.1