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

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Message-ID: <aTKnPvJUjGyyueH4@shell.armlinux.org.uk>
Date: Fri, 5 Dec 2025 09:34:54 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Yao Zi <ziyao@...root.org>, Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Frank <Frank.Sae@...or-comm.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Choong Yong Liang <yong.liang.choong@...ux.intel.com>,
	Chen-Yu Tsai <wens@...e.org>, Jisheng Zhang <jszhang@...nel.org>,
	Furong Xu <0x1207@...il.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Mingcong Bai <jeffbai@...c.io>,
	Kexy Biscuit <kexybiscuit@...c.io>, Runhua He <hua@...c.io>,
	Xi Ruoyao <xry111@...111.site>
Subject: 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:
> > 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?

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