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

[Sudeep Holla <sudeep.holla@kernel.org>]

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().
>

Reviewed-by: Sudeep Holla <sudeep.holla@kernel.org>

> Fixes: 33cd7123ac0b ("mailbox: reset txdone_method TXDONE_BY_POLL if client knows_txdone")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> Found by code inspection and only compile-tested.
> 
>  drivers/mailbox/mailbox.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> index efacd24a085d..cfc49cfb057c 100644
> --- a/drivers/mailbox/mailbox.c
> +++ b/drivers/mailbox/mailbox.c
> @@ -343,7 +343,7 @@ static void mbox_clean_and_put_channel(struct mbox_chan *chan)
>  	scoped_guard(spinlock_irqsave, &chan->lock) {
>  		chan->cl = NULL;
>  		chan->active_req = MBOX_NO_MSG;
> -		if (chan->txdone_method == MBOX_TXDONE_BY_ACK)
> +		if (chan->txdone_method == MBOX_TXDONE_BY_ACK && chan->mbox->txdone_poll)
>  			chan->txdone_method = MBOX_TXDONE_BY_POLL;
>  	}
>  
> -- 
> 2.56.0.385.gac671c819a-goog
> 

-- 
Regards,
Sudeep