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SubjectRe: [PATCH] reset: allow to pass NULL pointer to reset_control_put()
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Am Mittwoch, den 04.05.2016, 20:34 +0900 schrieb Masahiro Yamada:
> Hi Arnd,
>
> 2016-05-04 20:24 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
> > On Wednesday 04 May 2016 20:17:51 Masahiro Yamada wrote:
> >> Currently, reset_control_put() just returns for error pointer,
> >> but not for NULL pointer. This is not reasonable.
> >>
> >> Passing NULL pointer should be allowed as well to make failure path
> >> handling easier.
> >>
> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> >> ---
> >>
> >> drivers/reset/core.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> >> index 181b05d..7bb16d1 100644
> >> --- a/drivers/reset/core.c
> >> +++ b/drivers/reset/core.c
> >> @@ -288,7 +288,7 @@ EXPORT_SYMBOL_GPL(reset_control_get);
> >>
> >> void reset_control_put(struct reset_control *rstc)
> >> {
> >> - if (IS_ERR(rstc))
> >> + if (IS_ERR_OR_NULL(rstc))
> >> return;
> >>
> >> module_put(rstc->rcdev->owner);
> >
> > Using IS_ERR_OR_NULL() normally indicates that there is something
> > wrong with the API, or with the caller.
> >
> > What exactly is the idea behind treating an error pointer as a valid
> > input to reset_control_put() here? Maybe it should just test for
> > NULL?

The idea was that you could do
drvdata->rstc = reset_control_get(...)
in the probe() function and
reset_control_put(drvdata->rstc)
in remove() without having to check for IS_ERR(drvdata->rstc) again.
I'm not convinced this is necessarily a good idea though. To simplify
the teardown path we already have devm_reset_control_get().

> I thought about that a bit,
> but there might be some (not nice) drivers that rely on the current behavior.
> I did not want to break any boards with my patch.
>
> So, should it be
>
> if (!rstc)
> return;
> or, perhaps
>
> if (!rstc || WARN_ON_ONCE(IS_ERR(rstc)))
> return;
>
> ?

NULL is not a valid input to reset_control, reset_control_get(_optional)
should never return NULL.

I'd be in favor of turning this into

if (WARN_ON(IS_ERR_OR_NULL(rstc)))
return;

As far as I am aware, ehci-tegra is the only driver that currently makes
use of the IS_ERR(rstc) return in reset_control_put():

struct reset_control *usb1_reset;

usb1_reset = of_reset_control_get(phy_np, "usb");
if (IS_ERR(usb1_reset)) {
/* ... */
} else {
reset_control_assert(usb1_reset);
udelay(1);
reset_control_deassert(usb1_reset);
}
reset_control_put(usb1_reset);

That'd be trivial to fix.

regards
Philipp

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