linux-kernel - Re: [PATCH] mailbox: Allow NULL message sending

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Message-ID: <CABb+yY18OEvfc8DDUiZqVeQtkmwcOFCSTMT7KoXb1LVA3RuxdA@mail.gmail.com>
Date: Sun, 7 Dec 2025 15:56:35 -0600
From: Jassi Brar <jassisinghbrar@...il.com>
To: Joonwon Kang <joonwonkang@...gle.com>
Cc: jonathanh@...dia.com, linux-kernel@...r.kernel.org, sudeep.holla@....com, 
	thierry.reding@...il.com
Subject: Re: [PATCH] mailbox: Allow NULL message sending

On Wed, Dec 3, 2025 at 11:57 PM Joonwon Kang <joonwonkang@...gle.com> wrote:
>
> On Tue, Nov 25, 2025 at 11:00 PM Joonwon Kang <joonwonkang@...gle.com> wrote:
> > >
> > > Clients may want to send interrupt only without any useful message
> > > involved. Since the current mailbox framework does not allow NULL
> > > message sending(although it allows receiving it), the clients should
> > > allocate a dummy message buffer and pretend sending it. Besides, if
> > > the mailbox controller calls `mbox_chan_txdone()` when the client
> > > drivers happen to send NULL message anyway, it will result in unexpected
> > > results by making the tx status messed up. This commit lifts the
> > > limitation and allows the clients to send interrupt only without any
> > > message buffer allocated.
> > >
> > Interrupts without data messages are called 'doorbells' and we already
> > support them.
> > thanks
>
> I am not sure if it is already supported. Let me draw two cases which imply
> that it is not supported. If the cases make sense, could you reconsider the
> patch? If it is supported in another branch, could you refer me to that
> branch? I am currently referring to the `for-next` branch of your mailbox
> repo.
>
I believe you are talking about some hypothetical situation?
Otherwise, which controller is that?
A controller driver is supposed to either expect data or not, but not both.

thanks
-jassi