[Intel-wired-lan] [PATCH iwl-next 2/3] ice: use GENMASK instead of BIT(n) - 1 in pack functions

[Jacob Keller <jacob.e.keller@intel.com>]

The functions used to pack the Tx and Rx context into the hardware format
rely on using BIT() and then subtracting 1 to get a bitmask. These
functions even have a comment about how x86 machines can't use this method
for certain widths because the SHL instructions will not work properly.

The Linux kernel already provides the GENMASK macro for generating a
suitable bitmask. Further, GENMASK is capable of generating the mask
including the shift_width. Since width is the total field width, take care
to subtract one to get the final bit position.

Since we now include the shifted bits as part of the mask, shift the source
value first before applying the mask.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
---
 drivers/net/ethernet/intel/ice/ice_common.c | 44 ++++-----------------
 1 file changed, 8 insertions(+), 36 deletions(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_common.c b/drivers/net/ethernet/intel/ice/ice_common.c
index d8bcc8bd91d8..ffe44f2d3dc5 100644
--- a/drivers/net/ethernet/intel/ice/ice_common.c
+++ b/drivers/net/ethernet/intel/ice/ice_common.c
@@ -4373,14 +4373,11 @@ static void ice_pack_ctx_byte(u8 *src_ctx, u8 *dest_ctx,
 
 	/* prepare the bits and mask */
 	shift_width = ce_info->lsb % 8;
-	mask = (u8)(BIT(ce_info->width) - 1);
+	mask = GENMASK(ce_info->width - 1 + shift_width, shift_width);
 
 	src_byte = *from;
-	src_byte &= mask;
-
-	/* shift to correct alignment */
-	mask <<= shift_width;
 	src_byte <<= shift_width;
+	src_byte &= mask;
 
 	/* get the current bits from the target bit string */
 	dest = dest_ctx + (ce_info->lsb / 8);
@@ -4413,17 +4410,14 @@ static void ice_pack_ctx_word(u8 *src_ctx, u8 *dest_ctx,
 
 	/* prepare the bits and mask */
 	shift_width = ce_info->lsb % 8;
-	mask = BIT(ce_info->width) - 1;
+	mask = GENMASK(ce_info->width - 1 + shift_width, shift_width);
 
 	/* don't swizzle the bits until after the mask because the mask bits
 	 * will be in a different bit position on big endian machines
 	 */
 	src_word = *(u16 *)from;
-	src_word &= mask;
-
-	/* shift to correct alignment */
-	mask <<= shift_width;
 	src_word <<= shift_width;
+	src_word &= mask;
 
 	/* get the current bits from the target bit string */
 	dest = dest_ctx + (ce_info->lsb / 8);
@@ -4456,25 +4450,14 @@ static void ice_pack_ctx_dword(u8 *src_ctx, u8 *dest_ctx,
 
 	/* prepare the bits and mask */
 	shift_width = ce_info->lsb % 8;
-
-	/* if the field width is exactly 32 on an x86 machine, then the shift
-	 * operation will not work because the SHL instructions count is masked
-	 * to 5 bits so the shift will do nothing
-	 */
-	if (ce_info->width < 32)
-		mask = BIT(ce_info->width) - 1;
-	else
-		mask = (u32)~0;
+	mask = GENMASK(ce_info->width - 1 + shift_width, shift_width);
 
 	/* don't swizzle the bits until after the mask because the mask bits
 	 * will be in a different bit position on big endian machines
 	 */
 	src_dword = *(u32 *)from;
-	src_dword &= mask;
-
-	/* shift to correct alignment */
-	mask <<= shift_width;
 	src_dword <<= shift_width;
+	src_dword &= mask;
 
 	/* get the current bits from the target bit string */
 	dest = dest_ctx + (ce_info->lsb / 8);
@@ -4507,25 +4490,14 @@ static void ice_pack_ctx_qword(u8 *src_ctx, u8 *dest_ctx,
 
 	/* prepare the bits and mask */
 	shift_width = ce_info->lsb % 8;
-
-	/* if the field width is exactly 64 on an x86 machine, then the shift
-	 * operation will not work because the SHL instructions count is masked
-	 * to 6 bits so the shift will do nothing
-	 */
-	if (ce_info->width < 64)
-		mask = BIT_ULL(ce_info->width) - 1;
-	else
-		mask = (u64)~0;
+	mask = GENMASK_ULL(ce_info->width - 1 + shift_width, shift_width);
 
 	/* don't swizzle the bits until after the mask because the mask bits
 	 * will be in a different bit position on big endian machines
 	 */
 	src_qword = *(u64 *)from;
-	src_qword &= mask;
-
-	/* shift to correct alignment */
-	mask <<= shift_width;
 	src_qword <<= shift_width;
+	src_qword &= mask;
 
 	/* get the current bits from the target bit string */
 	dest = dest_ctx + (ce_info->lsb / 8);
-- 
2.41.0