linux-kernel - Re: [PATCH v9 5/9] mailbox: add CIX mailbox driver

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Message-ID: <CABb+yY3KBdA0KeExfzx6otJxOiXUYQC27gaw_+s5OpQxdUmp0Q@mail.gmail.com>
Date: Wed, 16 Jul 2025 12:15:07 -0500
From: Jassi Brar <jassisinghbrar@...il.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Guomin Chen <guomin.chen@...tech.com>, Rob Herring <robh@...nel.org>, krzk+dt@...nel.org, 
	Conor Dooley <conor+dt@...nel.org>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Peter Chen <peter.chen@...tech.com>, 
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, cix-kernel-upstream@...tech.com, 
	Marc Zyngier <maz@...nel.org>, Sudeep Holla <sudeep.holla@....com>, 
	Kajetan Puchalski <kajetan.puchalski@....com>, Enric Balletbo <eballetb@...hat.com>, 
	Gary Yang <gary.yang@...tech.com>, Lihua Liu <Lihua.Liu@...tech.com>
Subject: Re: [PATCH v9 5/9] mailbox: add CIX mailbox driver

On Wed, Jul 16, 2025 at 2:20 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Wed, Jul 16, 2025, at 04:28, Guomin chen wrote:
> > On Tue, Jul 15, 2025 at 05:11:01PM -0500, Jassi Brar wrote:
> >> On Mon, Jul 14, 2025 at 10:40 AM Arnd Bergmann <arnd@...db.de> wrote:
> >> > My main worry here is that the types are all quite different: while
> >> > the doorbell and fast mailboxes are what a lot of other drivers have,
> >> > the FIFO mode does not seem to be a good fit for the mailbox subsystem
> >> > but instead looks like a more generic firmware interface with variable
> >> > length messages.
> >> >
> >> > For those, I think a higher-level driver with fixed data structures
> >> > passed through the hardware interface seems more appropriate.
> >> >
> >> Yes. But sometimes when the data structures of a protocol are not
> >> bigger than FIFO depth, the platform may choose to use the FIFO mode.
> >> I see it as platform dependent.
> >>
> >> > Are there any other mailbox drivers that just use the mailbox to
> >> > tunnel variable-length messages?
> >> >
> >> From a quick look, Armada 37xx and Hi6220 have fifo though they fill
> >> them up fully for each transfer.
> >>
> > Yes, both Armada 37xx and Hi6220 support FIFO functionality, and they
> > fill the FIFO with each transfer.
> >
> > Since the cix mailbox hardware supports messages with a maximum length
> > of 128 bytes, different clients transmit messages of varying lengths,
> > such as the cix DSP using 8 bytes, the cix sensorhub using 12 bytes, etc.
> >
> > Therefore, the cix mailbox driver has been modified to support variable-
> > length messages of up to 128 bytes. This allows for more compact and
> > flexible support of various clients.
>
> Thanks, this makes sense to me, and I have no other objections if
> this is an established way to use the subsystem. I wonder if there
> is a way to abstract it further though, since it would appear that
> the same thing should be possible on any device that has a FIFO
> to buffer more than a single fixed-length message.
>
> Jassi, are there any remaining issues on your side that need to
> be fixed before merging the initial driver? It would be nice if I
> could merge all nine patches through the soc tree for 6.17 if the
> current version, or a feature-reduced variant of the mailbox
> driver is ok.
>
I have pointed out some, and Guomin said there is a revision coming.
That should be good.

-j