Re: Pericom PI7C9X2G608 (12d8: 2608) missing from ACS quirk — breaks Renesas uPD720202 USB3 cards when IOMMU is on

On Tue, Aug 11, 2026 at 05:57:33AM -0500, Max Stevens wrote:
> Hi Bjorn,
> 
> Thanks for the quick patch. I tested its effect on my PI7C9X2G608GP
> (12d8:2608) by replicating what pci_fixup_pericom_acs_store_forward()
> does, using setpci at runtime (I have not built a patched kernel —
> happy to do that too if you want a test of the actual binary).
> 
> Findings on the 2G608:
> 
> The mode register exists at the same offset as on the smaller
> switches: upstream port config 0x74. Value on my system before any
> test: 0x0102 (store-forward bit clear).
> With ACS on all four downstream ports set to what the kernel normally
> enables here (ACSCtl = SrcValid+ ReqRedir+ CmpltRedir+ UpstreamFwd+),
> and 0x74 bit 0 CLEAR, device enumeration on the downstream xHCI
> controllers fails: [43069.603242] xhci-pci-renesas 0000:0c:00.0: Error
> while assigning device slot ID: Command Aborted [43069.603270] usb
> usb9-port1: couldn't allocate usb_device
> Setting 0x74 to 0x0103 (bit 0, store-forward) with ACS unchanged, then
> rebinding the xHCI drivers: the same device on the same port
> enumerates immediately and works fully: [43071.971147] usb 9-1: new
> full-speed USB device number 2 using xhci-pci-renesas [43072.132176]
> usb 9-1: Product: Azeron Keypad [43072.218656] hid-generic
> 0003:16D0:113C.0017: input,hidraw12: USB HID v1.11 Keyboard [Azeron
> LTD Azeron Keypad] on usb-0000:0c:00.0-1/input1
> I toggled the bit back and forth across several driver rebinds. Every
> "Command Aborted" failure I have logged (both today and across earlier
> debugging) occurred with the bit clear; none with it set.
> 
> One honest nuance: with the bit clear the failure is not 100% — I saw
> one enumeration attempt start successfully during a bit-clear window.
> That intermittency is consistent with the load-dependent packet
> buffering behaviour described in Nathan's original erratum writeup,
> and with this card family's long history of "sometimes almost works"
> reports on various forums.

If it's an improvement, I think it's worth applying even if it's not a
100% fix.

> So on this hardware the store-forward workaround behaves exactly as it
> does on the already-quirked siblings, and the patch looks correct to
> me.
> 
> Tested-by: Maximo Paulino [email protected]

Thanks for doing this.  I'll queue up the patch below for v7.3 without
your explicit tested-by because quirks run at different times than
setpci, and the timing/ordering is often important.


commit c56a7c02e664 ("PCI: Add ACS quirk for Pericom PI7C9X2G404 switches [12d8:2608]")
Author: Bjorn Helgaas <[email protected]>
Date:   Mon Aug 10 20:20:26 2026 -0500

    PCI: Add ACS quirk for Pericom PI7C9X2G404 switches [12d8:2608]
    
    Max reported that PI7C9X2G608GP (12d8:2608), the 6-port variant, has the
    same erratum and makes an entire class of consumer USB 3.0 cards completely
    non-functional on any system with the IOMMU enabled.
    
    On a system with a StarTech PEXUSB3S44V-style 4-port USB 3.0 card With
    IOMMU on, ACS on the switch's downstream ports is enabled (ACSCtl:
    SrcValid+ ReqRedir+ CmpltRedir+ UpstreamFwd+). The four xHCI controllers
    then probe cleanly, register their buses, upload firmware, and report port
    connect status normally — but any device plugged into any port fails
    enumeration with:
    
      xhci-pci-renesas 0000:09:00.0: Error while assigning device slot ID: Command Aborted
      xhci-pci-renesas 0000:09:00.0: Max number of devices this xHCI host supports is 32.
      usb usb3-port1: couldn't allocate usb_device
    
    Apply the same workaround used for other related Pericom switches.
    
    Reported-by: Max Stevens <[email protected]>
    Closes: https://lore.kernel.org/all/CADoo8uyrmw_GkNgNf+bV_pieYN_gn5i49rOF8jUvSsfPOcqCJA@mail.gmail.com
    Signed-off-by: Bjorn Helgaas <[email protected]>


diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index b09f27f7846f..27f7d56c9ac3 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -6263,6 +6263,10 @@ DECLARE_PCI_FIXUP_ENABLE(PCI_VENDOR_ID_PERICOM, 0xb404,
 			 pci_fixup_pericom_acs_store_forward);
 DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_PERICOM, 0xb404,
 			 pci_fixup_pericom_acs_store_forward);
+DECLARE_PCI_FIXUP_ENABLE(PCI_VENDOR_ID_PERICOM, 0x2608,
+			 pci_fixup_pericom_acs_store_forward);
+DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_PERICOM, 0x2608,
+			 pci_fixup_pericom_acs_store_forward);
 
 static void nvidia_ion_ahci_fixup(struct pci_dev *pdev)
 {