AHCI interrupt acknowledge violates specification => fixed in SVN

[mav]

While optimizing FreeBSD AHCI driver I found that VirtualBox does not allow to acknowledge AHCI interrupt by writing AHCI IS (Interrupt Status) register without reading from that register first.

You may see it looking inside HbaInterruptStatus_r() function, which is the only place where u32PortsInterrupted variable is cleared. But in configuration with only one SATA port present and command completion coalescing disabled I don't really need to read IS register to know the source of the interrupt. So in my driver I am just writing to it without spending extra time on read, which can be quite expensive. It perfectly works on real hardware, but not inside VirtualBox.

I believe it is an AHCI specification violation from the VirtualBox side, and it should be fixed.

[aeichner]

Thanks for the report, this will be fixed in the next maintenance release.

[Frank Mehnert]

Fix is part of VBox 4.3.18.