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

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Date:   Thu, 23 Aug 2018 12:14:57 -0700
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     davem@...emloft.net
Cc:     Jacob Keller <jacob.e.keller@...el.com>, netdev@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com, jogreene@...hat.com,
        Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [net 07/13] ice: Use order_base_2 to calculate higher power of 2

From: Jacob Keller <jacob.e.keller@...el.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.

Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
Tested-by: Tony Brelinski <tonyx.brelinski@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---
 drivers/net/ethernet/intel/ice/ice_main.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
index f3ba4f76b6cb..3eff1d2d1543 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))) {
-- 
2.17.1