linux-kernel - Re: [PATCHv5 2/4] mailbox: Introduce framework for mailbox

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Date:	Mon, 2 Jun 2014 22:41:44 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Matt Porter <mporter@...aro.org>
Cc:	Jassi Brar <jaswinder.singh@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	lkml <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Anna, Suman" <s-anna@...com>,
	Loic Pallardy <loic.pallardy@...com>,
	LeyFoon Tan <lftan.linux@...il.com>,
	Craig McGeachie <slapdau@...oo.com.au>,
	Courtney Cavin <courtney.cavin@...ymobile.com>,
	Rob Herring <robherring2@...il.com>,
	Josh Cartwright <joshc@...eaurora.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Kumar Gala <galak@...eaurora.org>,
	"ks.giri@...sung.com" <ks.giri@...sung.com>
Subject: Re: [PATCHv5 2/4] mailbox: Introduce framework for mailbox

On Mon, Jun 2, 2014 at 8:44 PM, Matt Porter <mporter@...aro.org> wrote:
> On Fri, May 30, 2014 at 11:01:55AM +0530, Jassi Brar wrote:
>
>>  Being more specific to your platform, I think you need some server
>> code (mailbox's client) that every driver (like clock, pmu, pinmux
>> etc) registers with to send messages to remote and receive commands
>> from remote ... perhaps by registering some filter to sort out
>> messages for each driver.
>
> Right, and here's where you hit on the problem. This server you mention
> is not a piece of hardware, it would be a software construct. As such, it
> doesn't fit into the DT binding as it exists. It's probably best to
> illustrate in DT syntax.
>
> If I were to represent the hardware relationship in the DT binding now
> it would look like this:
>
> ---
> cpm: mailbox@...dbeef {
>         compatible = "brcm,bcm-cpm-mailbox";
>         reg = <...>;
>         #mbox-cells <1>;
>         interrupts = <...>;
> };
>
> /* clock complex */
> ccu {
>         compatible = "brcm,bcm-foo-ccu";
>         mbox = <&cpm CPM_SYSTEM_CHANNEL>;
>         mbox-names = "system";
>         /* leaving out other mailboxes for brevity */
>         #clock-cells <1>;
>         clock-output-names = "bar",
>                              "baz";
> };
>
> pmu {
>         compatible = "brcm,bcm-foo-pmu"
>         mbox = <&cpm CPM_SYSTEM_CHANNEL>;
>         mbox-names = "system";
> };
>
> pinmux {
>         compatible = "brcm,bcm-foo-pinctrl";
>         mbox = <&cpm CPM_SYSTEM_CHANNEL>;
>         mbox-names = "system";
> };
> ---
Yeah, I too don't think its a good idea.


> What we would need to do is completely ignore this information in each
> of the of the client drivers associated with the clock, pmu, and pinmux
> devices. This IPC server would need to be instantiated and get the
> mailbox information from some source. mbox_request_channel() only works
> when the client has an of_node with the mbox-names property present.
> Let's say we follow this model and represent it in DT:
>
> --
> cpm: mailbox@...dbeef {
>         compatible = "brcm,bcm-cpm-mailbox";
>         reg = <...>;
>         #mbox-cells <1>;
>         interrupts = <...>;
> };
>
> cpm_ipc {
>         compatible = "brcm,bcm-cpm-ipc";
>         mbox = <&cpm CPM_SYSTEM_CHANNEL>;
>         mbox-names = "system";
>         /* leaving out other mailboxes for brevity */
> };
> ---
>
> This would allow an ipc driver to exclusively own this system channel,
> but now we've invented a binding that doesn't reflect the hardware at
> all. It's describing software so I don't believe the DT maintainers will
> allow this type of construct.
>
Must the server node specify MMIO and an IRQ, to be acceptable? Like ...

cpm_ipc : cpm@...dbeef {
         compatible = "brcm,bcm-cpm-ipc";
       /*  reg = <0xdeadbeef 0x100>; */
       /*  interrupts = <0 123 4>;  */
         mbox = <&cpm CPM_SYSTEM_CHANNEL>;
         mbox-names = "system";
};

cpm_ipc already specifies a hardware resource (mbox) that its driver
needs, I think that should be enough reason. If it were some purely
soft property for the driver like
      mode = "poll";  //or "irq"
then the node wouldn't be justified because that is the job of a
build-time config or run-time module option.

Regards,
-Jassi
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