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SubjectRe: [PATCH v2 2/4] input: keyboard: tegra: use devm_* for resource allocation
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.

--
Dmitry


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