linux-kernel - Re: [PATCH] uio: uio_pdrv

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Date:	Thu, 10 Jul 2008 12:58:51 +0200
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
Cc:	Magnus Damm <magnus.damm@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"hjk@...utronix.de" <hjk@...utronix.de>,
	"lethal@...ux-sh.org" <lethal@...ux-sh.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] uio: uio_pdrv_genirq V2

On Thu, Jul 10, 2008 at 08:56:39AM +0200, Uwe Kleine-König wrote:
> > +
> > +static irqreturn_t uio_pdrv_genirq_handler(int irq, struct uio_info *dev_info)
> > +{
> > +       struct uio_pdrv_genirq_platdata *priv = dev_info->priv;
> > +       unsigned long flags;
> > +
> > +       /* Just disable the interrupt in the interrupt controller, and
> > +        * remember the state so we can allow user space to enable it later.
> > +        */
> > +       spin_lock_irqsave(&priv->lock, flags);
> > +       if (!priv->irq_disabled) {
> > +               disable_irq_nosync(irq);
> > +               priv->irq_disabled = 1;
> > +       }
> > +       spin_unlock_irqrestore(&priv->lock, flags);
> > +       return IRQ_HANDLED;
> > +}
> > +
> > +static int uio_pdrv_genirq_irqcontrol(struct uio_info *dev_info, s32 irq_on)
> > +{
> > +       struct uio_pdrv_genirq_platdata *priv = dev_info->priv;
> > +       unsigned long flags;
> > +
> > +       /* Allow user space to enable and disable the interrupt
> > +        * in the interrupt controller, but keep track of the
> > +        * state to prevent per-irq depth damage.
> > +        */
> > +
> > +       spin_lock_irqsave(&priv->lock, flags);
> > +       if (irq_on && priv->irq_disabled)
> > +               enable_irq(dev_info->irq);
> > +       else if (!irq_on && !priv->irq_disabled)
> > +               disable_irq(dev_info->irq);
> I'm not sure if this is a problem on SMP.  Should you use
> disable_irq_nosync here, too?  Probably it's OK.

*_nosync should not be needed, as he doesn't call irqcontrol from the irq
handler. But using the same lock in handler and irqcontrol presents a
problem, as Alan pointed out.

> 
> > +
> > +       priv->irq_disabled = !irq_on;
> > +       spin_unlock_irqrestore(&priv->lock, flags);
> > +       return 0;
> > +}
> 
> 
> > +       ret = uio_register_device(&pdev->dev, priv->uioinfo);
> > +       if (ret) {
> > +               dev_err(&pdev->dev, "unable to register uio device\n");
> > +               goto bad1;
> > +       }
> > +
> > +       platform_set_drvdata(pdev, priv);
> This should probably go before uio_register_device.  (Uups, this is an
> issue for uio_pdrv, too.)

Yes, because uio_register_device will enable the irq, and you might
arrive in the handler without having your platform data in place.

Thanks,
Hans

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