Message-ID: <CAPKp9uZTnWCojeZHyvrm=vTuY15dAHiW1CWP18JUfuKU-mfH0Q@mail.gmail.com>
Date:	Tue, 3 Jun 2014 10:35:16 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Jassi Brar <jassisinghbrar@...il.com>
Cc:	Matt Porter <mporter@...aro.org>,
	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

Hi Jassi,

On Mon, Jun 2, 2014 at 6:11 PM, Jassi Brar <jassisinghbrar@...il.com> wrote:
> 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.
>

Like Matt, I am also in similar situation where there's a lot of common
code necessary to construct/parse IPCs for each of the drivers using the
mailbox.

As per your suggestion if we have single DT node to specify both the
controller and the client, we might still have to pollute this node with
software specific compatibles.

One possible scenario I can think of is that if the mailbox controller is
a standard primecell like PL320 used in multiple SoCs, each SoC vendor
will develop their own protocol implemented in their firmware. This is true
even with single SoC vendor having same IP but changing the protocol to
talk to their firmware. We will need a way to identify that protocol mechanism.
Does it make sense to add that  ? Is that something acceptable ?

Regards,
Sudeep
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