Re: [PATCH 1/1] PCI/bwctrl: Disable BW controller on Intel P45 using a quirk

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jan 16, 2026 at 03:15:12PM +0200, Ilpo Järvinen wrote:
> The commit 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as
> PCIe BW controller") was found to lead to a boot hang on a Intel P45
> system. Testing without setting Link Bandwidth Management Interrupt
> Enable (LBMIE) and Link Autonomous Bandwidth Interrupt Enable (LABIE)
> (PCIe r7.0, sec. 7.5.3.7) in bwctrl allowed system to come up.
> 
> P45 is very old chipset and supports only up to gen2 PCIe, so not
> having bwctrl does not seem a huge defiancy.
> 
> Add no_bw_notif into the struct pci_dev and quirk Intel P45 Root Port
> with it.
> 
> Reported-by: Adam Stylinski <kungfujesus06@gmail.com>
> Link: https://lore.kernel.org/linux-pci/aUCt1tHhm_-XIVvi@eggsbenedict/
> Tested-by: Adam Stylinski <kungfujesus06@gmail.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Applied to pci/bwctrl for v6.20, thanks!

> ---
>  drivers/pci/pcie/bwctrl.c |  3 +++
>  drivers/pci/quirks.c      | 10 ++++++++++
>  include/linux/pci.h       |  1 +
>  3 files changed, 14 insertions(+)
> 
> diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
> index 36f939f23d34..4ae92c9f912a 100644
> --- a/drivers/pci/pcie/bwctrl.c
> +++ b/drivers/pci/pcie/bwctrl.c
> @@ -250,6 +250,9 @@ static int pcie_bwnotif_probe(struct pcie_device *srv)
>  	struct pci_dev *port = srv->port;
>  	int ret;
>  
> +	if (port->no_bw_notif)
> +		return -ENODEV;
> +
>  	/* Can happen if we run out of bus numbers during enumeration. */
>  	if (!port->subordinate)
>  		return -ENODEV;
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index b9c252aa6fe0..6ef42a2c4831 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -1359,6 +1359,16 @@ static void quirk_transparent_bridge(struct pci_dev *dev)
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL,	PCI_DEVICE_ID_INTEL_82380FB,	quirk_transparent_bridge);
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_TOSHIBA,	0x605,	quirk_transparent_bridge);
>  
> +/*
> + * Enabling Link Bandwidth Management Interrupts (BW notifications) can cause
> + * boot hangs on P45.
> + */
> +static void quirk_p45_bw_notifications(struct pci_dev *dev)
> +{
> +	dev->no_bw_notif = 1;
> +}
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x2e21, quirk_p45_bw_notifications);
> +
>  /*
>   * Common misconfiguration of the MediaGX/Geode PCI master that will reduce
>   * PCI bandwidth from 70MB/s to 25MB/s.  See the GXM/GXLV/GX1 datasheets
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 864775651c6f..3a556cd749e3 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -406,6 +406,7 @@ struct pci_dev {
>  						      user sysfs */
>  	unsigned int	clear_retrain_link:1;	/* Need to clear Retrain Link
>  						   bit manually */
> +	unsigned int	no_bw_notif:1;	/* BW notifications may cause issues */
>  	unsigned int	d3hot_delay;	/* D3hot->D0 transition time in ms */
>  	unsigned int	d3cold_delay;	/* D3cold->D0 transition time in ms */
>  
> 
> base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> -- 
> 2.39.5
>