linux-kernel - Re: [PATCH 3/6] mailbox: Add support for ST's Mailbox IP

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Message-ID: <20150724095249.GB3436@x1>
Date:	Fri, 24 Jul 2015 10:52:49 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Alexey Klimov <klimov.linux@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devicetree@...r.kernel.org, jassisinghbrar@...il.com,
	kernel@...inux.com
Subject: Re: [PATCH 3/6] mailbox: Add support for ST's Mailbox IP

On Thu, 23 Jul 2015, Alexey Klimov wrote:
> On Fri, Jul 17, 2015 at 3:04 PM, Lee Jones <lee.jones@...aro.org> wrote:
> > ST's platforms currently support a maximum of 5 Mailboxes, one for
> > each of the supported co-processors situated on the platform.  Each
> > Mailbox is divided up into 4 instances which consist of 32 channels.
> > Messages are passed between the application and co-processors using
> > shared memory areas.  It is the Client's responsibility to manage
> > these areas.
> >
> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > ---
> >  drivers/mailbox/Kconfig       |   7 +
> >  drivers/mailbox/Makefile      |   2 +
> >  drivers/mailbox/mailbox-sti.c | 562 ++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 571 insertions(+)
> >  create mode 100644 drivers/mailbox/mailbox-sti.c
> 
> [..]
> 
> > +static irqreturn_t sti_mbox_thread_handler(int irq, void *data)
> > +{
> > +       struct sti_mbox_device *mdev = data;
> > +       struct sti_mbox_pdata *pdata = dev_get_platdata(mdev->dev);
> > +       struct mbox_chan *chan;
> > +       unsigned int instance;
> > +
> > +       for (instance = 0; instance < pdata->num_inst; instance++) {
> > +keep_looking:
> > +               chan = sti_mbox_irq_to_channel(mdev, instance);
> > +               if (!chan)
> > +                       continue;
> > +
> > +               mbox_chan_received_data(chan, NULL);
> > +               sti_mbox_clear_irq(chan);
> > +               sti_mbox_enable_channel(chan);
> > +               goto keep_looking;
> > +       }
> > +
> > +       return IRQ_HANDLED;
> > +}
> > +
> > +static irqreturn_t sti_mbox_irq_handler(int irq, void *data)
> > +{
> > +       struct sti_mbox_device *mdev = data;
> > +       struct sti_mbox_pdata *pdata = dev_get_platdata(mdev->dev);
> > +       struct sti_channel *chan_info;
> > +       struct mbox_chan *chan;
> > +       unsigned int instance;
> > +       int ret = IRQ_NONE;
> > +
> > +       for (instance = 0; instance < pdata->num_inst; instance++) {
> > +               chan = sti_mbox_irq_to_channel(mdev, instance);
> > +               if (!chan)
> > +                       continue;
> > +               chan_info = chan->con_priv;
> > +
> > +               if (!sti_mbox_channel_is_enabled(chan)) {
> > +                       dev_warn(mdev->dev,
> > +                                "Unexpected IRQ: %s\n"
> > +                                "  instance: %d: channel: %d [enabled: %x]\n",
> > +                                mdev->name, chan_info->instance,
> > +                                chan_info->channel, mdev->enabled[instance]);
> > +                       ret = IRQ_HANDLED;
> > +                       continue;
> > +               }
> > +
> > +               sti_mbox_disable_channel(chan);
> > +               ret = IRQ_WAKE_THREAD;
> > +       }
> > +
> > +       if (ret == IRQ_NONE)
> > +               dev_err(mdev->dev, "Spurious IRQ - was a channel requested?\n");
> > +
> > +       return ret;
> > +}
> 
> With such usage of ret variable can it happen that handling of last
> but one channel/instance will set ret to IRQ_WAKE_THREAD and at the
> same time handling of last channel/instance will set ret to
> IRQ_HANDLED during iteration loop and finally generic subsystem will
> not wake up thread handler because it will receive IRQ_HANDLED?
> Just checking.

Yes, I guess that it theoretically possible.  Now fixed.

Thanks for the spot.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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