Subject: Re: [PATCH 0/5] mailbox: imx: Use threaded handler to avoid kworker in imx's remoteproc

From: Mathieu Poirier <[email-masked]>
Date: Tue, 2 Jun 2026 10:51:53 -0600

On Fri, May 29, 2026 at 06:01:02PM +0200, Sebastian Andrzej Siewior wrote:
> The imx's remoteproc driver uses a kworker from its mailbox callback to
> complete the request. The reason is that the imx mailbox driver invokes
> the callback from its interrupt handler and the remoteproc callback (at
> least the rpmsg-tty) requires a preemptible context.
> 
> This works but is problematic in a PREEMPT_RT environment where the
> latency of the invocation is important. By scheduling a kworker the
> high task priority from the threaded handler is lost and the kworker
> competes for CPU ressources with every SCHED_OTHER task in the system.
> This can lead to long delays on a busy system with other RT threads
> which are less important than the completion of this request.
> 
> Looking over other mailbox driver, like the arm_mhu for instance, they
> use a threaded interrupt handler to invoke the callback. This avoids the
> kworker detour.
> 
> The here suggested change utilises a threaded interrupt to invoke the
> callback. The primary handler mask the interrupt source so that the
> handler can run without getting interrupted by the interrupt again.
> Doing so avoids marking the interrupt IRQF_ONESHOT so that that in a
> shared-interrupt environment the other interrupt can still fire while
> the first one is masked.
> 
> This change was tested on a im93 board with rpmsg-tty driver.
> 
> Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
> ---
> Sebastian Andrzej Siewior (5):
>       mailbox: imx: Start splitting the IRQ handler in primary and threaded handler
>       mailbox: imx: Move the RX part of the mailbox into the threaded handler
>       mailbox: imx: Move the RXDB part of the mailbox into the threaded handler
>       mailbox: imx: Don't force-thread the primary handler
>       remoteproc: imx_rproc: Invoke the callback directly
> 
>  drivers/mailbox/imx-mailbox.c  | 65 +++++++++++++++++++++++++++++++++---------
>  drivers/remoteproc/imx_rproc.c | 33 +--------------------

For imx_rproc.c:

Reviewed-by: Mathieu Poirier <[email-masked]>

You may also want to fix driver/remoteproc/stm32_rproc.c

>  2 files changed, 53 insertions(+), 45 deletions(-)
> ---
> base-commit: 9e171fc1d7d7ab847a750c03571c87ac3c17bd84
> change-id: 20260529-imx_mbox_rproc-7d512f5a6f78
> 
> Best regards,
> -- 
> Sebastian Andrzej Siewior <[email-masked]>
>