dev-hsa: enable interruptible hsa signal support

dev-hsa: enable interruptible hsa signal support

Event creation and management support from emulated drivers is required
to support interruptible signals in HSA and this support was not
available. This changeset adds the event creation and management support
in the emulated driver.  With this patch, each interruptible signal
created by the HSA runtime is associated with a signal event. The HSA
runtime can then put a thread waiting on a signal condition to sleep
asking the driver to monitor the event associated with that signal. If
the signal is modified by the GPU, the dispatcher notifies the driver
about signal value change.  If the modifier is a CPU thread, the thread
will have to make HSA API calls to modify the signal and these API calls
will notify the driver about signal value change. Once the driver is
notified about a change in the signal value, the driver checks to see if
any thread is sleeping on that signal and wake up the sleeping thread
associated with that event. The driver has also implemented the time_out
wakeup that can wake up the thread after a certain time period has
expired. This is also true for barrier packets.

Each signal has an event address in a kernel managed and allocated
event page that can be used as a mailbox pointer to notify an event.
However, this feature used by non-CPU agents to communicate with the
driver is not implemented by this changeset because the non-CPU HSA
agents in our model can directly communicate with driver in our
implementation. Having said that, adding that feature should be trivial
because the event address and event pages are correctly setup by this
changeset and just adding the event page's virtual address to our PIO
doorbell interface in the page tables and registering that pio address
to the driver should be sufficient. Managing mailbox pointer for an
event is based on event ID and using this event ID as an index into
event page, this changeset already provides a unique mailbox pointer for
each event.

Change-Id: Ic62794076ddd47526b1f952fdb4c1bad632bdd2e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38335
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>