netdev - [PATCH RFC net-next 08/12] net: mtk_eth_soc: add fixme comment for state->speed use

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Message-Id: <E1nc6kx-004ikJ-CY@rmk-PC.armlinux.org.uk>
Date:   Wed, 06 Apr 2022 15:35:35 +0100
From:   "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
To:     Marek Behún <kabel@...nel.org>
Cc:     Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: [PATCH RFC net-next 08/12] net: mtk_eth_soc: add fixme comment for
 state->speed use

Add a fixme comment for the last remaining incorrect usage of
state->speed in the mac_config() method, which is strangely in a code
path which is only run when the PHY interface mode changes.

This means if we are in RGMII mode, changes in state->speed will not
cause the INTF_MODE, TRGMII_RCK_CTRL and TRGMII_TCK_CTRL registers to
be set according to the speed, nor will the TRGPLL clock be set to the
correct value.

Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index a16f02ed921a..b605a823dcd4 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -324,6 +324,14 @@ static void mtk_mac_config(struct phylink_config *config, unsigned int mode,
 							      state->interface))
 					goto err_phy;
 			} else {
+				/* FIXME: this is incorrect. Not only does it
+				 * use state->speed (which is not guaranteed
+				 * to be correct) but it also makes use of it
+				 * in a code path that will only be reachable
+				 * when the PHY interface mode changes, not
+				 * when the speed changes. Consequently, RGMII
+				 * is probably broken.
+				 */
 				mtk_gmac0_rgmii_adjust(mac->hw,
 						       state->interface,
 						       state->speed);
-- 
2.30.2