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

[Bjorn Helgaas]

[+to Philipp, Thomas for MSI devres question]

On Fri, Dec 05, 2025 at 09:34:54AM +0000, Russell King (Oracle) wrote:
> On Fri, Dec 05, 2025 at 05:31:34AM +0000, Yao Zi wrote:
> > On Mon, Nov 24, 2025 at 07:06:12PM +0000, Russell King (Oracle) wrote:
> > > On Mon, Nov 24, 2025 at 04:32:10PM +0000, Yao Zi wrote:
> > > > +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)
> > > > +{
> > > ...
> > > > +	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?