It's necessary to adjust the MAC TX clock when the linkspeed changes,
but it's noted such adjustment always fails on TH1520 SoC, and reading
back from APB glue registers that control clock generation results in
garbage, causing broken link.

With some testing, it's found a clock must be ungated for access to APB
glue registers. Without any consumer, the clock is automatically
disabled during late kernel startup. Let's get and enable it if it's
described in devicetree.

Fixes: 33a1a01e3afa ("net: stmmac: Add glue layer for T-HEAD TH1520 SoC")
Signed-off-by: Yao Zi <ziyao@disroot.org>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
index c72ee759aae5..95096244a846 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
@@ -211,6 +211,7 @@ static int thead_dwmac_probe(struct platform_device *pdev)
 	struct stmmac_resources stmmac_res;
 	struct plat_stmmacenet_data *plat;
 	struct thead_dwmac *dwmac;
+	struct clk *apb_clk;
 	void __iomem *apb;
 	int ret;
 
@@ -224,6 +225,11 @@ static int thead_dwmac_probe(struct platform_device *pdev)
 		return dev_err_probe(&pdev->dev, PTR_ERR(plat),
 				     "dt configuration failed\n");
 
+	apb_clk = devm_clk_get_optional_enabled(&pdev->dev, "apb");
+	if (IS_ERR(apb_clk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(apb_clk),
+				     "failed to get apb clock\n");
+
 	dwmac = devm_kzalloc(&pdev->dev, sizeof(*dwmac), GFP_KERNEL);
 	if (!dwmac)
 		return -ENOMEM;
-- 
2.50.1

On Tue, Jul 29, 2025 at 09:37:33AM +0000, Yao Zi wrote:
> It's necessary to adjust the MAC TX clock when the linkspeed changes,
> but it's noted such adjustment always fails on TH1520 SoC, and reading
> back from APB glue registers that control clock generation results in
> garbage, causing broken link.
> 
> With some testing, it's found a clock must be ungated for access to APB
> glue registers. Without any consumer, the clock is automatically
> disabled during late kernel startup. Let's get and enable it if it's
> described in devicetree.
> 
> Fixes: 33a1a01e3afa ("net: stmmac: Add glue layer for T-HEAD TH1520 SoC")
> Signed-off-by: Yao Zi <ziyao@disroot.org>
> ---
>  drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
> index c72ee759aae5..95096244a846 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
> @@ -211,6 +211,7 @@ static int thead_dwmac_probe(struct platform_device *pdev)
>  	struct stmmac_resources stmmac_res;
>  	struct plat_stmmacenet_data *plat;
>  	struct thead_dwmac *dwmac;
> +	struct clk *apb_clk;
>  	void __iomem *apb;
>  	int ret;
>  
> @@ -224,6 +225,11 @@ static int thead_dwmac_probe(struct platform_device *pdev)
>  		return dev_err_probe(&pdev->dev, PTR_ERR(plat),
>  				     "dt configuration failed\n");
>  
> +	apb_clk = devm_clk_get_optional_enabled(&pdev->dev, "apb");
> +	if (IS_ERR(apb_clk))
> +		return dev_err_probe(&pdev->dev, PTR_ERR(apb_clk),
> +				     "failed to get apb clock\n");
> +
>  	dwmac = devm_kzalloc(&pdev->dev, sizeof(*dwmac), GFP_KERNEL);
>  	if (!dwmac)
>  		return -ENOMEM;
> -- 
> 2.50.1
> 

Thank you for tracking down root cause and fixing it.

Reviewed-by: Drew Fustini <fustini@kernel.org>