The existing iaa crypto async support provides an implementation that
satisfies the interface but does so in a synchronous manner - it fills
and submits the IDXD descriptor and then waits for it to complete
before returning.  This isn't a problem at the moment, since all
existing callers (e.g. zswap) wrap any asynchronous callees in a
synchronous wrapper anyway.

This change makes the iaa crypto async implementation truly
asynchronous: it fills and submits the IDXD descriptor, then returns
immediately with -EINPROGRESS.  It also sets the descriptor's 'request
completion irq' bit and sets up a callback with the IDXD driver which
is called when the operation completes and the irq fires.  The
existing callers such as zswap use synchronous wrappers to deal with
-EINPROGRESS and so work as expected without any changes.

This mode can be enabled by writing 'async_irq' to the sync_mode
iaa_crypto driver attribute:

  echo async_irq > /sys/bus/dsa/drivers/crypto/sync_mode

Async mode without interrupts (caller must poll) can be enabled by
writing 'async' to it:

  echo async > /sys/bus/dsa/drivers/crypto/sync_mode

The default sync mode can be enabled by writing 'sync' to it:

  echo sync > /sys/bus/dsa/drivers/crypto/sync_mode

The sync_mode value setting at the time the IAA algorithms are
registered is captured in each algorithm's crypto_ctx and used for all
compresses and decompresses when using a given algorithm.
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>