Hi Mathias,
On 1/2/2023 8:38 AM, Mathias Nyman wrote:
On 29.12.2022 23.14, Wesley Cheng wrote:
Hi Mathias,
On 12/28/2022 7:47 AM, Mathias Nyman wrote:
On 24.12.2022 1.31, Wesley Cheng wrote:
Implement the XHCI operations for allocating and requesting for a
secondary
interrupter. The secondary interrupter can allow for events for a
particular endpoint to be routed to a separate event ring. The event
routing is defined when submitting a transfer descriptor to the USB HW.
There is a specific field which denotes which interrupter ring to
route the
event to when the transfer is completed.
An example use case, such as audio packet offloading can utilize a
separate
event ring, so that these events can be routed to a different processor
within the system. The processor would be able to independently submit
transfers and handle its completions without intervention from the main
processor.
Adding support for more xHCI interrupters than just the primary one
make sense for
both the offloading and virtualization cases.
xHCI support for several interrupters was probably added to support
virtualization,
to hand over usb devices to virtual machines and give them their own
event ring and
MSI/MSI-X vector.
In this offloading case you probably want to avoid xHC interrupts
from this device
completely, making sure it doesn't wake up the main CPU unnecessarily.
So is the idea here to let xhci driver set up the new interrupter,
its event ring,
and the endpoint transfer rings. Then pass the address of the
endpoint transfer rings
and the new event ring to the separate processor.
This separate processor then both polls the event ring for new
events, sets its dequeue
pointer, clears EHB bit, and queues new TRBs on the transfer ring.
so xhci driver does not handle any events for the audio part, and no
audio data URBs
are sent to usb core?
Your entire description is correct. To clarify, the interfaces which
are non-audio will still be handled by the main processor. For
example, a USB headset can have a HID interface as well for volume
control. The HID interface will still be handled by the main
processor, and events routed to the main event ring.
How about the control part?
Is the control endpoint for this device still handled normally by usb
core/xhci?
Control transfers are always handled on the main processor. Only
audio interface's endpoints.
Good to know, that means interrupter should be chosen per endpoint, not
per device.
For the xhci parts I think we should start start by adding generic
support for several
interrupters, then add parts needed for offloading.
I can split up the patchsets to add interrupters first, then adding
the offloading APIs in a separate patch.
I started looking at supporting secondary interrupters myself.
Let me work on that part a bit first. We have a bit different end goals.
I want to handle interrupts from a secondary interrupter, while this
audio offload
really just wants to mask some interrupts.
I was looking at how we could possibly split up the XHCI secondary
interrupter, and offloading parts. Since the XHCI secondary interrupter
is a feature that is defined in the XHCI spec (and we aren't doing
anything outside of what is defined), I was thinking of having a
separate XHCI driver (ie xhci-sec.c/h) that can be used to define all
APIs related to setting up the event ring and ring management.
(interrupt support can be added here) This aligns a bit with what Alan
suggested, and removing the APIs in the USB HCD, since this is XHCI
specific stuff. (
https://lore.kernel.org/linux-usb/Y6zwZOquZOTZfnvP@xxxxxxxxxxxxxxxxxxx/ )
For the offloading part, I think this is a bit more dependent on how
different platforms implement it. To use more of a generic approach
like how Albert suggested here:
https://patchwork.kernel.org/project/linux-usb/list/?series=704174
Basically to give vendors the ability to define their own
sequences/callbacks, and from which the XHCI driver will call into. (if
needed) These would need to be a separate set of XHCI drivers as well.
Do you think this is a proper model for us to go with, so that we can
allow for vendors to easily add functionality? Appreciate the inputs.
Thanks
Wesley Cheng
