Re: [PATCH] PCI: Disable MSI for ULi M1575 EHCI controller

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Wed, Sep 30, 2026 at 09:10:58PM +0200, Imre Kaloz wrote:
> With MSI, the ULi M1575 EHCI controller (10b9:5239) intermittently stops
> executing its asynchronous schedule. Control transfers time out ("device
> not accepting address", "device descriptor read/64"), the port is handed
> to the companion OHCI controller and the device ends up at full speed. On
> a configured hub the stall shows up as hub descriptor and status read
> failures. Only re-initializing the controller recovers it.
> 
> On a Sun Ultra 45, 65 of 800 controller initializations stalled with MSI
> and none of 200 with INTx. Each initialization is an unbind and bind of
> ehci-pci on the EHCI function, with MSI or INTx selected through its
> msi_bus attribute; with this quirk, 0 of 100 cycles of the same loop
> stalled. The stall reproduces on a kernel that already contains
> commit 0b60557230ad ("usb: ehci: Prevent missed ehci interrupts with
> edge-triggered MSI").
> 
> The OHCI functions (10b9:5237) keep MSI. They showed no stall, and the
> hub enumerated through them on MSI during the EHCI failures, so only the
> EHCI function is quirked.
> 
> The illumos EHCI driver also disables MSI on this chip, in
> ehci_register_intrs_and_init_mutex() in
> usr/src/uts/common/io/usb/hcd/ehci/ehci_util.c.
> 
> Until USB HCDs started trying MSI first in v5.9, the controller always
> used INTx. Disable MSI so it uses INTx again on this chipset.

Since it's tested on real HW, the quirk makes sense.
Thanks for report and the fix!
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko