ACPI / EC: Add asynchronous command byte write support

Move the first command byte write into advance_transaction() so that all
EC register accesses that can affect the command processing state machine
can happen in this asynchronous state machine advancement function.

The advance_transaction() function then can be a complete implementation
of an asyncrhonous transaction for a single command so that:
 1. The first command byte can be written in the interrupt context;
 2. The command completion waiter can also be used to wait the first command
    byte's timeout;
 3. In BURST mode, the follow-up command bytes can be written in the
    interrupt context directly, so that it doesn't need to return to the
    task context. Returning to the task context reduces the throughput of
    the BURST mode and in the worst cases where the system workload is very
    high, this leads to the hardware driven automatic BURST mode exit.

In order not to increase memory consumption, convert 'done' into 'flags'
to contain multiple indications:
 1. ACPI_EC_COMMAND_COMPLETE: converting from original 'done' condition,
    indicating the completion of the command transaction.
 2. ACPI_EC_COMMAND_POLL: indicating the availability of writing the first
    command byte. A new command can utilize this flag to compete for the
    right of accessing the underlying hardware. There is a follow-up bug
    fix that has utilized this new flag.

The 2 flags are important because it also reflects a key concept of IO
programs' design used in the system softwares. Normally an IO program
running in the kernel should first be implemented in the asynchronous way.
And the 2 flags are the most common way to implement its synchronous
operations on top of the asynchronous operations:
1. POLL: This flag can be used to block until the asynchronous operations
         can happen.
2. COMPLETE: This flag can be used to block until the asynchronous
             operations have completed.
By constructing code cleanly in this way, many difficult problems can be
solved smoothly.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=70891
Link: https://bugzilla.kernel.org/show_bug.cgi?id=63931
Link: https://bugzilla.kernel.org/show_bug.cgi?id=59911
Reported-and-tested-by: Gareth Williams <gareth@garethwilliams.me.uk>
Reported-and-tested-by: Hans de Goede <jwrdegoede@fedoraproject.org>
Reported-by: Barton Xu <tank.xuhan@gmail.com>
Tested-by: Steffen Weber <steffen.weber@gmail.com>
Tested-by: Arthur Chen <axchen@nvidia.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

0 files changed, 0 insertions, 0 deletions