Re: [PATCH] mailbox: Only reset txdone_method to POLL if controller supports polling

[Peng Fan <peng.fan@oss.nxp.com>]

On Tue, Nov 03, 2026 at 04:42:36PM -0800, Douglas Anderson wrote:
>In mbox_controller_register(), a mailbox controller's default
>txdone_method is initialized to MBOX_TXDONE_BY_IRQ if mbox->txdone_irq
>is set, MBOX_TXDONE_BY_POLL if mbox->txdone_poll is set, or
>MBOX_TXDONE_BY_ACK if neither is set. Only controllers with
>mbox->txdone_poll set initialize mbox->poll_hrt and require
>mbox->ops->last_tx_done to be implemented.
>
>When a client with cl->knows_txdone = true binds to a channel whose
>controller uses MBOX_TXDONE_BY_POLL, __mbox_bind_client() overrides
>chan->txdone_method to MBOX_TXDONE_BY_ACK. Commit 33cd7123ac0b
>("mailbox: reset txdone_method TXDONE_BY_POLL if client knows_txdone")
>attempted to restore chan->txdone_method to MBOX_TXDONE_BY_POLL when
>the channel is released, but did so unconditionally whenever
>chan->txdone_method == MBOX_TXDONE_BY_ACK:
>
>  if (chan->txdone_method == MBOX_TXDONE_BY_ACK)
>          chan->txdone_method = MBOX_TXDONE_BY_POLL;
>
>For controllers whose native txdone_method is MBOX_TXDONE_BY_ACK
>(!txdone_irq && !txdone_poll), releasing a channel (or failing in the
>controller's startup() callback) corrupts chan->txdone_method to
>MBOX_TXDONE_BY_POLL even though the controller does not support
>polling and has not initialized poll_hrt or ops->last_tx_done.
>
>Check chan->mbox->txdone_poll before resetting chan->txdone_method to
>MBOX_TXDONE_BY_POLL in mbox_clean_and_put_channel().
>
>Fixes: 33cd7123ac0b ("mailbox: reset txdone_method TXDONE_BY_POLL if client knows_txdone")
>Signed-off-by: Douglas Anderson <dianders@chromium.org>
>---

LGTM:
Reviewed-by: Peng Fan <peng.fan@nxp.com>