linux-kernel - Re: [PATCH] mailbox: add support for doorbell/signal mode controllers

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Message-ID: <CABb+yY2so2aYK4v6LKgW_jQhyig1-TWW-fLgH0b-1mTxaTaUmg@mail.gmail.com>
Date:   Thu, 2 Nov 2017 08:26:42 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] mailbox: add support for doorbell/signal mode controllers

On Thu, Nov 2, 2017 at 3:42 AM, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
> On Wed 01 Nov 11:03 PDT 2017, Jassi Brar wrote:
>> On Wed, Nov 1, 2017 at 10:02 PM, Sudeep Holla <sudeep.holla@....com> wrote:
> [..]
>> >
>> > This is rough idea I have on extending mailbox interface to support
>> > the doorbell requirements.
>> >
>> What doorbell requirements does the api not support?
>> QComm's APCS IPC is what you call a "doorbell" controller and is
>> already supported by the API. It could run SCMI even easier than MHU
>> (your controller).
>>
>
> I agree; from a mbox consumer perspective a doorbell should be a mailbox
> channel that when signalled will ring the bell, i.e. the message is not
> significant and should not be provided by the client.
>
> If the message is significant and is not derived from the mailbox
> channel (e.g. channel id -> bit in register) it is not a mailbox
> doorbell, it's s regular mailbox used as a doorbell.
>
>
> The potential improvement I see in the Qualcomm case is to wrap the
> mbox_send_message(chan, NULL); mbox_client_txdone(chan, 0); calls in one
> simple "mbox_ring_door_bell(chan)" - but I haven't investigated the
> validity of this as a generic function.
>
If you remember I already suggested we can use the existing api to
define a convenient helper ->
https://www.spinics.net/lists/linux-soc/msg01781.html

mailbox_client.h
*******************
void mbox_ring_doorbell(struct mbox_chan *chan, void *mssg)
{
   (void)mbox_send_message(chan, mssg);
   mbox_client_txdone(chan, 0);
}

.... instead of adding a new api and modifying each driver.

Cheers!