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

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Message-ID: <20250805173825.0f70f9cd@kernel.org>
Date: Tue, 5 Aug 2025 17:38:25 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Yao Zi <ziyao@...root.org>
Cc: 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>, Paolo Abeni
 <pabeni@...hat.com>, Emil Renner Berthing
 <emil.renner.berthing@...onical.com>, Jisheng Zhang <jszhang@...nel.org>,
 nux-riscv@...ts.infradead.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: stmmac: thead: Enable TX clock before MAC
 initialization

On Fri,  1 Aug 2025 09:45:07 +0000 Yao Zi wrote:
> 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.

All the possible DIV values are valid?
I think it's safer to set the DIV to some well known constant, 
just to be on the safe side.