linux-kernel - [PATCH] igc: optimize igc_ptp_systim_to

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Message-Id: <20210827171515.2518713-1-trix@redhat.com>
Date:   Fri, 27 Aug 2021 10:15:15 -0700
From:   trix@...hat.com
To:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        davem@...emloft.net, kuba@...nel.org
Cc:     intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tom Rix <trix@...hat.com>
Subject: [PATCH] igc: optimize igc_ptp_systim_to_hwtstamp()

From: Tom Rix <trix@...hat.com>

Static analysis reports this representative problem
igc_ptp.c:676:3: warning: The left operand of '+' is a garbage value
                ktime_add_ns(shhwtstamps.hwtstamp, adjust);
                ^            ~~~~~~~~~~~~~~~~~~~~

The issue is flagged because the setting of shhwtstamps is
in igc_ptp_systim_to_hwtstamp() it is set only in one path through
this switch.

	switch (adapter->hw.mac.type) {
	case igc_i225:
		memset(hwtstamps, 0, sizeof(*hwtstamps));
		/* Upper 32 bits contain s, lower 32 bits contain ns. */
		hwtstamps->hwtstamp = ktime_set(systim >> 32,
						systim & 0xFFFFFFFF);
		break;
	default:
		break;
	}

Changing the memset the a caller initialization is a small optimization
and will resolve uninitialized use issue.

A switch statement with one case is overkill, convert to an if statement.

This function is small and only called once, change to inline for an
expected small runtime and size improvement.

Signed-off-by: Tom Rix <trix@...hat.com>
---
 drivers/net/ethernet/intel/igc/igc_ptp.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_ptp.c b/drivers/net/ethernet/intel/igc/igc_ptp.c
index 0f021909b430a0..1443a2da246e22 100644
--- a/drivers/net/ethernet/intel/igc/igc_ptp.c
+++ b/drivers/net/ethernet/intel/igc/igc_ptp.c
@@ -417,20 +417,14 @@ static int igc_ptp_verify_pin(struct ptp_clock_info *ptp, unsigned int pin,
  * We need to convert the system time value stored in the RX/TXSTMP registers
  * into a hwtstamp which can be used by the upper level timestamping functions.
  **/
-static void igc_ptp_systim_to_hwtstamp(struct igc_adapter *adapter,
-				       struct skb_shared_hwtstamps *hwtstamps,
-				       u64 systim)
+static inline void igc_ptp_systim_to_hwtstamp(struct igc_adapter *adapter,
+					      struct skb_shared_hwtstamps *hwtstamps,
+					      u64 systim)
 {
-	switch (adapter->hw.mac.type) {
-	case igc_i225:
-		memset(hwtstamps, 0, sizeof(*hwtstamps));
-		/* Upper 32 bits contain s, lower 32 bits contain ns. */
+	/* Upper 32 bits contain s, lower 32 bits contain ns. */
+	if (adapter->hw.mac.type == igc_i225)
 		hwtstamps->hwtstamp = ktime_set(systim >> 32,
 						systim & 0xFFFFFFFF);
-		break;
-	default:
-		break;
-	}
 }
 
 /**
@@ -645,7 +639,7 @@ void igc_ptp_tx_hang(struct igc_adapter *adapter)
 static void igc_ptp_tx_hwtstamp(struct igc_adapter *adapter)
 {
 	struct sk_buff *skb = adapter->ptp_tx_skb;
-	struct skb_shared_hwtstamps shhwtstamps;
+	struct skb_shared_hwtstamps shhwtstamps = { 0 };
 	struct igc_hw *hw = &adapter->hw;
 	int adjust = 0;
 	u64 regval;
-- 
2.26.3