mailbox/omap: Add ti,mbox-send-noirq quirk to fix AM33xx CPU Idle

The mailbox framework controls the transmission queue and requires
either its controller implementations or clients to run the state
machine for the Tx queue. The OMAP mailbox controller uses a Tx-ready
interrupt as the equivalent of a Tx-done interrupt to run this Tx
queue state-machine.

The WkupM3 processor on AM33xx and AM43xx SoCs is used to offload
certain PM tasks, like doing the necessary operations for Device
PM suspend/resume or for entering lower c-states during cpuidle.

The CPUIdle on AM33xx requires the messages to be sent without
having to trigger the Tx-ready interrupts, as the interrupt
would immediately terminate the CPUIdle operation. Support for
this has been added by introducing a DT quirk, "ti,mbox-send-noirq"
and using it to modify the normal OMAP mailbox controller behavior
on the sub-mailboxes used to communicate with the WkupM3 remote
processor. This also requires the wkup_m3_ipc driver to adjust
its mailbox usage logic to run the Tx state machine.

NOTE:
- AM43xx does not communicate with WkupM3 for CPU Idle, so is
  not affected by this behavior. But, it uses the same IPC driver
  for PM suspend/resume functionality, so requires the quirk as
  well, because of changes to the common wkup_m3_ipc driver.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
[s-anna@ti.com: revise logic and update comments/patch description]
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/mailbox/omap-mailbox.txt b/Documentation/devicetree/bindings/mailbox/omap-mailbox.txt
index d1a043339c11..9b40c4925aa9 100644
--- a/Documentation/devicetree/bindings/mailbox/omap-mailbox.txt
+++ b/Documentation/devicetree/bindings/mailbox/omap-mailbox.txt
@@ -75,6 +75,14 @@ data that represent the following:
     Cell #3 (usr_id)  - mailbox user id for identifying the interrupt line
                         associated with generating a tx/rx fifo interrupt.
 
+Optional Properties:
+--------------------
+- ti,mbox-send-noirq:   Quirk flag to allow the client user of this sub-mailbox
+                        to send messages without triggering a Tx ready interrupt,
+                        and to control the Tx ticker. Should be used only on
+                        sub-mailboxes used to communicate with WkupM3 remote
+                        processor on AM33xx/AM43xx SoCs.
+
 Mailbox Users:
 ==============
 A device needing to communicate with a target processor device should specify