This change addresses an edge case that trips up macOS guest drivers
for PCI based XHCI controllers. The guest driver would attempt to
schedule events to XHCI event rings 1 and 2 even when using PCI
pin-based interrupts. Interrupts would therefore be dropped, and events
only handled on timeout.
So, in addition to disabling interrupter mapping if numintrs is 1, a
callback is added to xhci to check whether interrupter mapping should be
enabled. The PCI XHCI device type now provides an implementation of
this callback if the new "conditional-intr-mapping" property is enabled.
(default: disabled) When enabled, interrupter mapping is only enabled
when MSI-X or MSI is active.
This means that when using pin-based interrupts, events are only
submitted to interrupter 0 regardless of selected target. This allows
the macOS guest drivers to work with the device in those configurations.
Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2705
Message-ID: <20241227121336.25838-6-phil@philjordan.eu>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
9422a5acf2