netdev - Re: [PATCH net-next v6 2/3] net: axienet: Preparatory changes for dmaengine support

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Date: Tue, 19 Sep 2023 10:52:15 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Radhey Shyam Pandey <radhey.shyam.pandey@....com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, robh+dt@...nel.org,
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
	michal.simek@....com, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, git@....com,
	Sarath Babu Naidu Gaddam <sarath.babu.naidu.gaddam@....com>
Subject: Re: [PATCH net-next v6 2/3] net: axienet: Preparatory changes for
 dmaengine support

On Tue, Sep 19, 2023 at 12:46:54AM +0530, Radhey Shyam Pandey wrote:
> +/**
> + * axienet_open - Driver open routine.
> + * @ndev:	Pointer to net_device structure
> + *
> + * Return: 0, on success.
> + *	    non-zero error value on failure
> + *
> + * This is the driver open routine. It calls phylink_start to start the
> + * PHY device.
> + * It also allocates interrupt service routines, enables the interrupt lines
> + * and ISR handling. Axi Ethernet core is reset through Axi DMA core. Buffer
> + * descriptors are initialized.
> + */
> +static int axienet_open(struct net_device *ndev)
> +{
> +	int ret;
> +	struct axienet_local *lp = netdev_priv(ndev);
> +
> +	dev_dbg(&ndev->dev, "%s\n", __func__);
> +
> +	/* When we do an Axi Ethernet reset, it resets the complete core
> +	 * including the MDIO. MDIO must be disabled before resetting.
> +	 * Hold MDIO bus lock to avoid MDIO accesses during the reset.
> +	 */
> +	axienet_lock_mii(lp);
> +	ret = axienet_device_reset(ndev);
> +	axienet_unlock_mii(lp);
> +
> +	ret = phylink_of_phy_connect(lp->phylink, lp->dev->of_node, 0);
> +	if (ret) {
> +		dev_err(lp->dev, "phylink_of_phy_connect() failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	phylink_start(lp->phylink);

... and at this point, the link can come up while phylink_start() is
completing. Could that cause a problem if this happens before:

> +
> +	if (!lp->use_dmaengine) {
> +		ret = axienet_init_legacy_dma(ndev);
> +		if (ret)
> +			goto error_code;
> +	}

?

I suppose I should add this statement to the phylink_start()
documentation so that this point is clear for everyone.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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