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Date:   Fri, 4 Nov 2022 16:32:08 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     Sriranjani P <sriranjani.p@samsung.com>
Cc:     peppe.cavallaro@st.com, alexandre.torgue@foss.st.com,
        joabreu@synopsys.com, davem@davemloft.net, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, mcoquelin.stm32@gmail.com,
        richardcochran@gmail.com, netdev@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Chandrasekar R <rcsekar@samsung.com>,
        Suresh Siddha <ssiddha@tesla.com>
Subject: Re: [PATCH 2/4] net: stmmac: dwc-qos: Add FSD EQoS support
Message-ID: <Y2UweBsUDvrU9keT@lunn.ch>
References: <20221104120517.77980-1-sriranjani.p@samsung.com>
 <CGME20221104115854epcas5p4ca280f9c4cc4d1fa564d80016e9f0061@epcas5p4.samsung.com>
 <20221104120517.77980-3-sriranjani.p@samsung.com>
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> For FSD SoC, a mux switch is needed between internal and external clocks.
> By default after reset internal clock is used but for receiving packets
> properly, external clock is needed. Mux switch to external clock happens
> only when the external clock is present.


> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -3831,6 +3831,9 @@ static int __stmmac_open(struct net_device *dev,
>  	netif_tx_start_all_queues(priv->dev);
>  	stmmac_enable_all_dma_irq(priv);
>  
> +	if (priv->plat->rxmux_setup)
> +		priv->plat->rxmux_setup(priv->plat->bsp_priv, true);
> +
>  	return 0;
>  
>  irq_error:
> @@ -3884,6 +3887,9 @@ static int stmmac_release(struct net_device *dev)
>  	struct stmmac_priv *priv = netdev_priv(dev);
>  	u32 chan;
>  
> +	if (priv->plat->rxmux_setup)
> +		priv->plat->rxmux_setup(priv->plat->bsp_priv, false);
> +

Is this the code which is deciding if the external clock is present? So when somebody called
'ip link set eth42 up'?

Where is the external clock coming from?

      Andrew