Re: [PATCH v2 2/4] input: keyboard: tegra: use devm_* for resourceallocation

[Laxman Dewangan]

On Sunday 06 January 2013 04:48 AM, Dmitry Torokhov wrote:
> On Sat, Jan 05, 2013 at 04:50:58PM +0530, Laxman Dewangan wrote:
> > HI Dmitry,
> > Thanks for quick review.
> >
> > I will take care of your comment in next version. Some have my answer.
> >
> >
> > On Saturday 05 January 2013 01:36 PM, Dmitry Torokhov wrote:
> > > Hi Laxman,
> > >
> > > On Sat, Jan 05, 2013 at 01:15:08PM +0530, Laxman Dewangan wrote:
> > > > Use devm_* for memory, clock, input device allocation. This reduces
> > > > code for freeing these resources.
> > > >   	err = tegra_kbd_setup_keymap(kbc);
> > > > -	if (err) {
> > > > +	if (err < 0) {
> > > Why is this change? As far as I can see tegra_kbd_setup_keymap() never
> > > returns positive values.
> > Ok, mostly errors are in negative and hence this change, I will
> > revert it and will keep original.
> >
> > > >   		dev_err(&pdev->dev, "failed to setup keymap\n");
> > > > -		goto err_put_clk;
> > > > +		return err;
> > > >   	}
> > > >   	__set_bit(EV_REP, input_dev->evbit);
> > > > @@ -790,15 +784,15 @@ static int tegra_kbc_probe(struct platform_device *pdev)
> > > >   	err = request_irq(kbc->irq, tegra_kbc_isr,
> > > >   			  IRQF_NO_SUSPEND | IRQF_TRIGGER_HIGH, pdev->name, kbc);
> > > > -	if (err) {
> > > > +	if (err < 0) {
> > > Neither request_irq(). BTW, why not devm_request_irq?
> > I understand from Mark B on different patches that using
> > devm_request_irq() can create race condition when removing device.
> > Interrupt can occur when device resource release is in process and
> > so it can cause isr call which can use the freed pointer.
> > devm_request_irq() should be avoided.
> devm_request_irq() has a potential of creating a race condition, but it
> depents on the driver. In this particular case tegra driver ensures that
> interrupts are inhibited when input device is unregistered by providing
> tegra_kbc_close() method, so in this particular case it is safe to
> use devm_request_irq().
>
> Also, when using managed input devices, the unregistering and final
> freeing is a 2-step process, so even in absence of close() method, if
> initialization sequence was:
>
> 	devm_input_allocate_device()
> 	...
> 	devm_request_irq()
> 	...
> 	input_unregister_device()
>
> then order of freeing resources (behind the scenes) will be
>
> 	devm_input_device_unregister();
> 	/* input device is still present in memory and can
> 	 * handle input_event() calls.
> 	 */
> 	free_irq();
> 	devm_input_device_release();
>
> So using managed request_irq() _together_ with managed input devices is
> OK.

Thanks for detail explanation. I will modify and sent the new version of 
patch.

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