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

-----Original Message-----
From: Russell King <linux@armlinux.org.uk>
Sent: Tuesday, September 19, 2023 3:22 PM
To: Pandey, Radhey Shyam <radhey.shyam.pandey@amd.com>
Cc: davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
pabeni@redhat.com; robh+dt@kernel.org;
krzysztof.kozlowski+dt@linaro.org; conor+dt@kernel.org; Simek, Michal
[off-list ref]; netdev@vger.kernel.org;
devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-
kernel@lists.infradead.org; git (AMD-Xilinx) [off-list ref]; Sarath Babu
Naidu Gaddam [off-list ref]
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:

quoted

+/**
+ * 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);

quoted

+		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:

This preparatory patch keeps same execution sequence and it only 
creates wrapper around dma specific initialization. No functional
change.

There shouldn't be any problem if link come up while phylink_start is 
completing. Packet will be processed only after dma initialization
(Interrupts are enabled) . 

quoted

+
+	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.

Seems to be a good idea to capture it in documentation.

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