linux-kernel - Re: [RFC PATCH] mailbox: omap-mailbox: Flush out pending msgs before entering suspend

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Message-ID: <d8662d13-40bd-053b-6761-1a0ff7404782@ti.com>
Date: Thu, 23 Oct 2025 12:18:27 -0500
From: Hari Nagalla <hnagalla@...com>
To: Beleswar Prasad Padhi <b-padhi@...com>, Andrew Davis <afd@...com>,
        <jassisinghbrar@...il.com>, <linux-kernel@...r.kernel.org>
CC: <hiagofranco@...il.com>, <u-kumar1@...com>
Subject: Re: [RFC PATCH] mailbox: omap-mailbox: Flush out pending msgs before
 entering suspend

On 10/22/25 23:38, Beleswar Prasad Padhi wrote:
>> I'm still not convinced just throwing out messages is the correct thing
>> to do here, but for now at very least let's print some warning here when
>> messages get zapped.
> 
> I am also considering:
> 1. Mailbox queues for RTOS-RTOS communication could be
> firewalled for safety/FFI usecases. In that case, the above flush
> would result in an exception.
Yes, flushing all mailbox messages during suspend is not a good 
solution, as there can be in flight RTOS-RTOS communications for non 
participating cores.
> 2. This driver is common to OMAP SoCs which supported proper
> suspend/resume, meaning those rprocs could consume pending
> messages in resume. So clearing out messages from Linux
> might not be the best thing to do here.
> 
> What else can we do here? Should we just fallback to letting
> Linux see only it's required queues for IPC? By setting
> "ti,mbox-num-fifos = <4>"?
This makes the assumption that the first 4 FIFOs of the mailbox are 
used? and why 4? are you assuming first 2 for Linux IPC and next 2 for 
RTOS-RTOS communications?

How about, let the mailbox driver simply save and restore the config 
registers and ignore the FIFO messages? i.e if they are lost with the 
main domain going into OFF, so be it. Let the remote cores handle any 
missing messages. More often the remote cores may start afresh after a 
suspend to RAM.