netdev - [PATCH v2 net-next] e1000e: Remove duplicated writel() in e1000_configure

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Message-ID: <20240906021719.37754-1-takamitz@amazon.co.jp>
Date: Fri, 6 Sep 2024 11:17:19 +0900
From: Takamitsu Iwai <takamitz@...zon.co.jp>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Tony Nguyen <anthony.l.nguyen@...el.com>, "Przemek
 Kitszel" <przemyslaw.kitszel@...el.com>
CC: Takamitsu Iwai <takamitz@...zon.co.jp>, <netdev@...r.kernel.org>,
	<intel-wired-lan@...ts.osuosl.org>, Kohei Enju <enjuk@...zon.com>
Subject: [PATCH v2 net-next] e1000e: Remove duplicated writel() in e1000_configure_tx/rx()

Duplicated register initialization codes exist in e1000_configure_tx()
and e1000_configure_rx().

For example, writel(0, tx_ring->head) writes 0 to tx_ring->head, which
is adapter->hw.hw_addr + E1000_TDH(0).

This initialization is already done in ew32(TDH(0), 0).

ew32(TDH(0), 0) is equivalent to __ew32(hw, E1000_TDH(0), 0). It
executes writel(0, hw->hw_addr + E1000_TDH(0)). Since variable hw is
set to &adapter->hw, it is equal to writel(0, tx_ring->head).

We can remove similar four writel() in e1000_configure_tx() and
e1000_configure_rx().

commit 0845d45e900c ("e1000e: Modify Tx/Rx configurations to avoid
null pointer dereferences in e1000_open") has introduced these
writel(). This commit moved register writing to
e1000_configure_tx/rx(), and as result, it caused duplication in
e1000_configure_tx/rx().

This patch modifies the sequence of register writing, but removing
these writes is safe because the same writes were already there before
the commit.

I also have checked the datasheets [0] [1] and have not found any
description that we need to write RDH, RDT, TDH and TDT registers
twice at initialization. Furthermore, we have tested this patch on an
I219-V device physically.

Link: https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/82577-gbe-phy-datasheet.pdf [0]
Link: https://www.intel.com/content/www/us/en/content-details/613460/intel-82583v-gbe-controller-datasheet.html [1]
Tested-by: Kohei Enju <enjuk@...zon.com>
Signed-off-by: Takamitsu Iwai <takamitz@...zon.co.jp>
---

v1->v2
modify commit message to explain the reason why we can remove these writes safely.

v1 link
https://lore.kernel.org/netdev/20240902061454.85744-1-takamitz@amazon.co.jp/

 drivers/net/ethernet/intel/e1000e/netdev.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
index da5c59daf8ba..89c57be89c88 100644
--- a/drivers/net/ethernet/intel/e1000e/netdev.c
+++ b/drivers/net/ethernet/intel/e1000e/netdev.c
@@ -2928,11 +2928,8 @@ static void e1000_configure_tx(struct e1000_adapter *adapter)
 	tx_ring->head = adapter->hw.hw_addr + E1000_TDH(0);
 	tx_ring->tail = adapter->hw.hw_addr + E1000_TDT(0);

-	writel(0, tx_ring->head);
 	if (adapter->flags2 & FLAG2_PCIM2PCI_ARBITER_WA)
 		e1000e_update_tdt_wa(tx_ring, 0);
-	else
-		writel(0, tx_ring->tail);

 	/* Set the Tx Interrupt Delay register */
 	ew32(TIDV, adapter->tx_int_delay);
@@ -3253,11 +3250,8 @@ static void e1000_configure_rx(struct e1000_adapter *adapter)
 	rx_ring->head = adapter->hw.hw_addr + E1000_RDH(0);
 	rx_ring->tail = adapter->hw.hw_addr + E1000_RDT(0);

-	writel(0, rx_ring->head);
 	if (adapter->flags2 & FLAG2_PCIM2PCI_ARBITER_WA)
 		e1000e_update_rdt_wa(rx_ring, 0);
-	else
-		writel(0, rx_ring->tail);

 	/* Enable Receive Checksum Offload for TCP and UDP */
 	rxcsum = er32(RXCSUM);
-- 
2.40.1