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[07/13] ice: Use order_base_2 to calculate higher power of 2

Message ID 20180723173752.19676-8-anirudh.venkataramanan@intel.com
State Changes Requested
Delegated to: Jeff Kirsher
Headers show
Series Bug fixes for ice | expand

Commit Message

Anirudh Venkataramanan July 23, 2018, 5:37 p.m. UTC
From: Jacob Keller <jacob.e.keller@intel.com>

Currently, we use a combination of ilog2 and is_power_of_2() to
calculate the next power of 2 for the qcount. This appears to be causing
a warning on some combinations of GCC and the Linux kernel:

MODPOST 1 modules
WARNING: "____ilog2_NaN" [ice.ko] undefined!

This appears to because because GCC realizes that qcount could be zero
in some circumstances and thus attempts to link against the
intentionally undefined ___ilog2_NaN function.

The order_base_2 function is intentionally defined to return 0 when
passed 0 as an argument, and thus will be safe to use here.

This not only fixes the warning but makes the resulting code slightly
cleaner, and is really what we should have used originally.

Also update the comment to make it more clear that we are rounding up,
not just incrementing the ilog2 of qcount unconditionally.

Without this patch, we get warnings when building against the upstream

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
[Anirudh Venkataramanan <anirudh.venkataramanan@intel.com> minor cleanup for upstream submission]
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
 drivers/net/ethernet/intel/ice/ice_main.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)
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diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
index 81b04e1d7ea2..feeca75912ec 100644
--- a/drivers/net/ethernet/intel/ice/ice_main.c
+++ b/drivers/net/ethernet/intel/ice/ice_main.c
@@ -1313,11 +1313,8 @@  static void ice_vsi_setup_q_map(struct ice_vsi *vsi, struct ice_vsi_ctx *ctxt)
 		qcount = numq_tc;
-	/* find higher power-of-2 of qcount */
-	pow = ilog2(qcount);
-	if (!is_power_of_2(qcount))
-		pow++;
+	/* find the (rounded up) power-of-2 of qcount */
+	pow = order_base_2(qcount);
 	for (i = 0; i < ICE_MAX_TRAFFIC_CLASS; i++) {
 		if (!(vsi->tc_cfg.ena_tc & BIT(i))) {