linux-kernel - Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver

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Date:   Wed, 10 May 2017 12:00:46 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     Jeffrey Hugo <jhugo@...eaurora.org>,
        Andy Gross <andy.gross@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver

On Tue 09 May 19:33 PDT 2017, Jassi Brar wrote:

> On Wed, May 10, 2017 at 12:41 AM, Bjorn Andersson
> <bjorn.andersson@...aro.org> wrote:
> > On Tue 09 May 09:41 PDT 2017, Jassi Brar wrote:
[..]
> > The part where this piece of hardware differs from the other mailboxes
> > is that TX is done as send_data() returns and in the realm of the
> > mailbox there is no such thing as "tx done". So how about we extend the
> > framework to handle stateless and message-less doorbells?
> >
> This is a very common usecase. It would be unfair to other platforms
> to modify the API just because you find it awkward to call
> mbox_client_txdone() right after mbox_send_message(). For example,
> drivers/firmware/tegra/bpmp.c
> I'd much rather have mbox_send_message_and_tick() than implant a new api.
> 

I wasn't proposing to implement a new API; for mailbox controllers with
tx method set to POLL the client will only have call mbox_send_data()
nothing else. So I proposed [1] yesterday, that will make the apcs
controller behave just like this case.

Looking at it again, making sure that tx method is TXDONE_BY_ACK should
make mbox_client_txdone() essentially a nop, only locking the channel
spinlock twice and then returning, as send_data() didn't leave any data
in the queue. Is my understanding of this correct?

So please let me know what you think about [1], if you don't like it
I'll fix the things pointed to by Stephen and we'll have to live with
the two calls.

[1] https://patchwork.kernel.org/patch/9718931/

Regards,
Bjorn