linux-kernel - Re: [PATCH v2 01/15] mailbox: Deprecate NULL mbox messages; Introduce mbox_ring

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Message-ID: <CABb+yY2GbPcuPiVsE_-HCS8MbpBqvjgjDkoVLNSBDZq1bnfpEw@mail.gmail.com>
Date: Mon, 9 Feb 2026 18:38:58 -0600
From: Jassi Brar <jassisinghbrar@...il.com>
To: Douglas Anderson <dianders@...omium.org>
Cc: Frank.Li@....com, andersson@...nel.org, arm-scmi@...r.kernel.org, 
	cristian.marussi@....com, festevam@...il.com, imx@...ts.linux.dev, 
	jay.buddhabhatti@....com, jonathanh@...dia.com, kernel@...gutronix.de, 
	konradybcio@...nel.org, krzk@...nel.org, lenb@...nel.org, 
	linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-remoteproc@...r.kernel.org, linux-tegra@...r.kernel.org, 
	mathieu.poirier@...aro.org, michal.simek@....com, nm@...com, 
	rafael@...nel.org, robh@...nel.org, s.hauer@...gutronix.de, 
	shawn.guo@...aro.org, ssantosh@...nel.org, sudeep.holla@...nel.org, 
	tglx@...nel.org, thierry.reding@...il.com
Subject: Re: [PATCH v2 01/15] mailbox: Deprecate NULL mbox messages; Introduce mbox_ring_doorbell()

Hi Douglas,

On Sat, Feb 7, 2026 at 10:04 PM Douglas Anderson <dianders@...omium.org> wrote:
> @@ -249,6 +255,28 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
>         if (!chan || !chan->cl)
>                 return -EINVAL;
>
> +       /*
> +        * The mailbox core gets confused when mbox_send_message() is called
> +        * with NULL messages since the code directly stores messages in
> +        * `active_req` and assumes that a NULL `active_req` means no request
> +        * is active. This causes the core to call the mailbox controller a
> +        * second time even if the previous message hasn't finished and also
> +        * means the client's tx_done() callback will never be called. However,
> +        * clients historically passed NULL anyway. Deprecate passing NULL
> +        * here by adding a warning.
> +        *
> +        * Clients who don't have a message should switch to using
> +        * mbox_ring_doorbell(), which explicitly documents the immediate
> +        * sending of doorbells, the lack of txdone, and what happens if you
> +        * mix doorbells and normal messages.
> +        *
> +        * TODO: when it's certain that all clients have transitioned, consider
> +        * changing this to return -EINVAL.
> +        */
> +       if (!mssg)
> +               dev_warn_once(chan->mbox->dev,
> +                             "NULL mailbox messages are deprecated\n");
>
Nit: maybe  "NULL mailbox messages are deprecated, use
mbox_ring_doorbell instead" ?

Thanks,
Jassi