Re: [PATCH net-next v3 2/3] net: stmmac: Add glue driver for Motorcomm YT6801 ethernet controller

On Fri, Dec 05, 2025 at 05:31:34AM +0000, Yao Zi wrote:

Hi Russell,

Sorry for the late reply,

On Mon, Nov 24, 2025 at 07:06:12PM +0000, Russell King (Oracle) wrote:

quoted

On Mon, Nov 24, 2025 at 04:32:10PM +0000, Yao Zi wrote:

quoted

+static int motorcomm_setup_irq(struct pci_dev *pdev,
+			       struct stmmac_resources *res,
+			       struct plat_stmmacenet_data *plat)
+{
+	int ret;
+
+	ret = pci_alloc_irq_vectors(pdev, 6, 6, PCI_IRQ_MSIX);
+	if (ret > 0) {
+		res->rx_irq[0]	= pci_irq_vector(pdev, 0);
+		res->tx_irq[0]	= pci_irq_vector(pdev, 4);
+		res->irq	= pci_irq_vector(pdev, 5);
+
+		plat->flags |= STMMAC_FLAG_MULTI_MSI_EN;
+
+		return 0;
+	}
+
+	dev_info(&pdev->dev, "failed to allocate MSI-X vector: %d\n", ret);
+	dev_info(&pdev->dev, "try MSI instead\n");
+
+	ret = pci_alloc_irq_vectors(pdev, 1, 1, PCI_IRQ_MSI);
+	if (ret < 0)
+		return dev_err_probe(&pdev->dev, ret,
+				     "failed to allocate MSI\n");
+
+	res->irq = pci_irq_vector(pdev, 0);
+
+	return 0;
+}
+
+static int motorcomm_probe(struct pci_dev *pdev, const struct pci_device_id *id)
+{

...

quoted

+	ret = motorcomm_setup_irq(pdev, &res, plat);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "failed to setup IRQ\n");
+
+	motorcomm_init(priv);
+
+	res.addr = priv->base + GMAC_OFFSET;
+
+	return stmmac_dvr_probe(&pdev->dev, plat, &res);

If stmmac_dvr_probe() fails, then it will return an error code. This
leaves the PCI MSI interrupt allocated...

This isn't true. MSI API is a little magical: when the device is enabled
through pcim_enable_device(), the device becomes devres-managed, and
a plain call to pci_alloc_irq_vectors() becomes managed, too, even if
its name doesn't indicate it's a devres-managed API.

pci_free_irq_vectors() will be automatically called on driver deattach.
See pcim_setup_msi_release() in drivers/pci/msi/msi.c, which is invoked
by pci_alloc_irq_vectors() internally.

This looks very non-intuitive, and the documentation for
pci_alloc_irq_vectors() doesn't help:

 * Upon a successful allocation, the caller should use pci_irq_vector()
 * to get the Linux IRQ number to be passed to request_threaded_irq().
 * The driver must call pci_free_irq_vectors() on cleanup.
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

because if what you say is correct (and it looks like it is) then this
line is blatently incorrect.

Bjorn?

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