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

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Message-ID: <CABb+yY26R_DHQUhpg-xUR_Z7EnjdR_4LPai0M-vfFTAOZy=vvQ@mail.gmail.com>
Date: Tue, 15 Jul 2025 17:11:01 -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 Mon, Jul 14, 2025 at 10:40 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Sun, Jul 13, 2025, at 19:00, Jassi Brar wrote:
> > On Tue, Jul 8, 2025 at 8:54 AM Guomin chen <guomin.chen@...tech.com> wrote:
> > ....
> >> > > +/* [0~7] Fast channel
> >> > > + * [8] doorbell base channel
> >> > > + * [9]fifo base channel
> >> > > + * [10] register base channel
> >> > > + */
> >> > > +#define MBOX_FAST_IDX          7
> >> > > +#define MBOX_DB_IDX            8
> >> > > +#define MBOX_FIFO_IDX          9
> >> > > +#define MBOX_REG_IDX           10
> >> > > +#define CIX_MBOX_CHANS         11
> >> > > +
> >> > if it is not really a single controller owning different channels,
> >> > maybe implement only what you currently use.
> >> >
> >> As mentioned in the previous email, a single controller can support
> >> multiple different channels.
> >>
> > OK. I am not too worried about having all variants in one driver esp
> > when it is manageable and share the code.
> > Unless I am overlooking something. Arnd?
>
> 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.

Thanks