linux-kernel - [PATCH net] net: stmmac: thead: Enable TX clock before MAC initialization

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Message-ID: <20250801094507.54011-1-ziyao@disroot.org>
Date: Fri,  1 Aug 2025 09:45:07 +0000
From: Yao Zi <ziyao@...root.org>
To: Drew Fustini <fustini@...nel.org>,
	Guo Ren <guoren@...nel.org>,
	Fu Wei <wefu@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Emil Renner Berthing <emil.renner.berthing@...onical.com>,
	Jisheng Zhang <jszhang@...nel.org>
Cc: nux-riscv@...ts.infradead.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yao Zi <ziyao@...root.org>
Subject: [PATCH net] net: stmmac: thead: Enable TX clock before MAC initialization

The clk_tx_i clock must be supplied to the MAC for successful
initialization. On TH1520 SoC, the clock is provided by an internal
divider configured through GMAC_PLLCLK_DIV register when using RGMII
interface. However, currently we don't setup the divider before
initialization of the MAC, resulting in DMA reset failures if the
bootloader/firmware doesn't enable the divider,

[    7.839601] thead-dwmac ffe7060000.ethernet eth0: Register MEM_TYPE_PAGE_POOL RxQ-0
[    7.938338] thead-dwmac ffe7060000.ethernet eth0: PHY [stmmac-0:02] driver [RTL8211F Gigabit Ethernet] (irq=POLL)
[    8.160746] thead-dwmac ffe7060000.ethernet eth0: Failed to reset the dma
[    8.170118] thead-dwmac ffe7060000.ethernet eth0: stmmac_hw_setup: DMA engine initialization failed
[    8.179384] thead-dwmac ffe7060000.ethernet eth0: __stmmac_open: Hw setup failed

Let's simply write GMAC_PLLCLK_DIV_EN to GMAC_PLLCLK_DIV to enable the
divider before MAC initialization. The rate doesn't matter, which we
could reclock properly according to the link speed later after link is
up.

Signed-off-by: Yao Zi <ziyao@...root.org>
Fixes: 33a1a01e3afa ("net: stmmac: Add glue layer for T-HEAD TH1520 SoC")
---

Note that the DMA reset failures cannot be reproduced with the vendor
U-Boot, which always enables the divider, regardless whether the port is
used[1].

As this schema (enables the divider first and reclock it later) requires
access to the APB glue registers, the patch depends on v2 of series
"Fix broken link with TH1520 GMAC when linkspeed changes"[2] to ensure
the APB bus clock is ungated.

[1]: https://github.com/revyos/thead-u-boot/blob/93ff49d9f5bbe7942f727ab93311346173506d27/board/thead/light-c910/light.c#L581-L582
[2]: https://lore.kernel.org/netdev/20250801091240.46114-1-ziyao@disroot.org/

 drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
index 95096244a846..a65c2443bf42 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
@@ -164,6 +164,7 @@ static int thead_dwmac_enable_clk(struct plat_stmmacenet_data *plat)
 	case PHY_INTERFACE_MODE_RGMII_RXID:
 	case PHY_INTERFACE_MODE_RGMII_TXID:
 		/* use pll */
+		writel(GMAC_PLLCLK_DIV_EN, dwmac->apb_base + GMAC_PLLCLK_DIV);
 		writel(GMAC_GTXCLK_SEL_PLL, dwmac->apb_base + GMAC_GTXCLK_SEL);
 		reg = GMAC_TX_CLK_EN | GMAC_TX_CLK_N_EN | GMAC_TX_CLK_OUT_EN |
 		      GMAC_RX_CLK_EN | GMAC_RX_CLK_N_EN;
-- 
2.50.1