linux-kernel - Re: [PATCH v5 1/4] dt-bindings: mailbox: Document Hi6220 mailbox driver

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Date:	Mon, 1 Feb 2016 21:46:39 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Leo Yan <leo.yan@...aro.org>
Cc:	Rob Herring <robh@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Arnd Bergmann <arnd@...db.de>, Wei Xu <xuwei5@...ilicon.com>,
	Tyler Baker <tyler.baker@...aro.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Chen Feng <puck.chen@...ilicon.com>,
	Bintian Wang <bintian.wang@...wei.com>,
	Devicetree List <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Haojian Zhuang <haojian.zhuang@...aro.org>
Subject: Re: [PATCH v5 1/4] dt-bindings: mailbox: Document Hi6220 mailbox driver

On Mon, Feb 1, 2016 at 8:53 PM, Leo Yan <leo.yan@...aro.org> wrote:
> Hi Rob,
>
> Thanks for reviewing, please see below inline comments.
>
> On Mon, Feb 01, 2016 at 08:08:28AM -0600, Rob Herring wrote:
>> On Mon, Feb 01, 2016 at 09:34:44PM +0800, Leo Yan wrote:
>> > Document DT binding for Hisilicon Hi6220 mailbox driver.
>> >
>> > Signed-off-by: Leo Yan <leo.yan@...aro.org>
>> > ---
>> >  .../bindings/mailbox/hisilicon,hi6220-mailbox.txt  | 90 ++++++++++++++++++++++
>> >  1 file changed, 90 insertions(+)
>> >  create mode 100644 Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt
>> >
>> > diff --git a/Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt b/Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt
>> > new file mode 100644
>> > index 0000000..96e6acc
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt
>> > @@ -0,0 +1,90 @@
>> > +Hisilicon Hi6220 Mailbox Driver
>> > +===============================
>> > +
>> > +Hisilicon Hi6220 mailbox supports up to 32 channels. Each channel
>> > +is unidirectional with a maximum message size of 8 words. I/O is
>> > +performed using register access (there is no DMA) and the cell
>> > +raises an interrupt when messages are received.
>> > +
>> > +Mailbox Device Node:
>> > +====================
>> > +
>> > +Required properties:
>> > +--------------------
>> > +- compatible:              Shall be "hisilicon,hi6220-mbox"
>> > +- reg:                     Contains the mailbox register address range (base
>> > +                   address and length); the first item is for IPC
>> > +                   registers, the second item is shared buffer for
>> > +                   slots.
>> > +- #mbox-cells              Common mailbox binding property to identify the number
>> > +                   of cells required for the mailbox specifier. Should be 1.
>> > +- interrupts:              Contains the interrupt information for the mailbox
>> > +                   device. The format is dependent on which interrupt
>> > +                   controller the SoCs use.
>> > +
>> > +Optional Properties:
>> > +--------------------
>> > +- hi6220,mbox-tx-noirq: Flag to allow the client user of this mailbox driver
>> > +                   to send messages without triggering a TX completion
>> > +                   interrupt.
>>
>> I don't think this belongs in DT. This should be a flag the client
>> driver sets when it sends messages.
>
> The client driver can set "tx_block = true" so use this flag indicates
> the client thread should be blocked until data is transmitted.
>
Yes, but the 'tx_block' feature is provided by the core. The
controller driver should not need to know how the client works.

> But low level mailbox driver can use two method to support "tx_block"
> mode:
>
No, as I said, provider shouldn't care about consumers..

> - One method is to avoid using interrupt and mailbox framework will
>   poll with mailbox's idle flag which is set by remote processor
>   automatically;
> - Another method is to use interrupt to notify data has been
>   transmitted and interrupt handler will call completion function to
>   wake up blocked client thread;
>
If it is possible to have either 'idle flag set' or irq generated (not
both) by the remote, then you may sell the hi6220,mbox-tx-noirq
property as a "f/w feature" ... but still not for the sake of
tx_block.


>> > +
>> > +Child Nodes:
>> > +============
>> > +A child node is used for representing the actual sub-mailbox device that is
>> > +used for the communication between the host processor and a remote processor.
>> > +Each child node should have a unique node name across all the different
>> > +mailbox device nodes.
>> > +
>> > +Required properties:
>> > +--------------------
>> > +- hi6220,mbox-tx:  sub-mailbox descriptor property defining Tx channel
>> > +- hi6220,mbox-rx:  sub-mailbox descriptor property defining Rx channel
>> > +
>> > +Sub-mailbox Descriptor Data
>> > +---------------------------
>> > +Each of the above hi6220,mbox-tx and hi6220,mbox-rx properties should have 3
>> > +cells of data that represent the following:
>> > +    Cell #1 (slot_id) - mailbox slot id used either for transmitting
>> > +                        (hi6220,mbox-tx) or for receiving (hi6220,mbox-rx)
>> > +    Cell #2 (dst_irq) - irq identifier index number which used by MCU.
>> > +    Cell #3 (ack_irq) - irq identifier index number with generating a tx/rx
>> > +                        interrupt to application processor, mailbox driver
>> > +                        used this id to acknowledge interrupt.
>> > +
>> > +Example:
>> > +--------
>> > +
>> > +   mailbox: mailbox@...10000 {
>> > +           #mbox-cells = <1>;
>> > +           compatible = "hisilicon,hi6220-mbox";
>> > +           reg = <0x0 0xF7510000 0x0 0x1000>, /* IPC_S */
>> > +                 <0x0 0x06DFF800 0x0 0x0800>; /* Mailbox */
>> > +           interrupt-parent = <&gic>;
>> > +           interrupts = <GIC_SPI 94 IRQ_TYPE_LEVEL_HIGH>;
>> > +           mbox_stub_clock: mbox_stub_clock {
>> > +                   hi6220,mbox-rx = <0 1 10>;
>> > +                   hi6220,mbox-tx = <1 0 11>;
>
This looks like meant for the client node...
         mbox-names = "mbox-tx", "mbox-rx";
         mboxes = <&mailbox 1 0 11>, <&mailbox 0 1 10>;