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We are seeing a number of crashes in SMM, when VT-d is enabled while
'Legacy USB support' is enabled in various BIOSes.
The BIOS is supposed to indicate which addresses it uses for DMA in a
special ACPI table ("RMRR"), so that we can punch a hole for it when we
set up the IOMMU.
The problem is, as usual, that BIOS engineers are totally incompetent.
They write code which will crash if the DMA goes AWOL, and then they
either neglect to provide an RMRR table at all, or they put the wrong
addresses in it. And of course they don't do _any_ QA, since that would
take too much time away from their crack-smoking habit.
The real fix, of course, is for consumers to refuse to buy motherboards
which only have closed-source firmware available. If we had _open_
firmware, bugs like this would be easy to fix.
Since that's something I can only dream about, this patch implements an
alternative -- ensuring that the USB controllers are handed off from the
BIOS and quiesced _before_ the IOMMU is initialised. That would have
been a much better design than this RMRR nonsense in the first place, of
course. The bootloader has no business doing DMA after the OS has booted
anyway.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("khubd").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.