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

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Date:   Fri, 5 May 2017 11:37:29 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     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 Fri 05 May 03:26 PDT 2017, Jassi Brar wrote:

> On Fri, May 5, 2017 at 1:35 AM, Bjorn Andersson
> <bjorn.andersson@...aro.org> wrote:
> 
> > +
> > +static int qcom_apcs_ipc_send_data(struct mbox_chan *chan, void *data)
> > +{
> > +       struct qcom_apcs_ipc *apcs = container_of(chan->mbox,
> > +                                                 struct qcom_apcs_ipc, mbox);
> > +       unsigned long idx = (unsigned long)chan->con_priv;
> > +
> > +       writel(BIT(idx), apcs->base + apcs->offset);
> > +
> When/how does this bit get ever cleared again?
> You may want to add last_tx_done() callback to check if this bit is
> cleared before you can send the next interrupt. And set
> txdone_poll/irq accordingly.
> 

It's a write-only register, writing a bit fires off an edge triggered
interrupt on the specific remote processor, which will ack the
associated IRQ status and handle the interrupt.

As the "message" is just a notification to the other side that it needs
to act on "something", there's no harm in notifying it multiple times
before it has a chance to ack the IRQ and a write after that will be
seen as a separate interrupt.

Regards,
Bjorn