linux-kernel - Re: [PATCH v1] reset: Make optional stuff optional for all users

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Date:   Mon, 03 Apr 2017 18:23:24 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Ramiro.Oliveira@...opsys.com" <Ramiro.Oliveira@...opsys.com>
Subject: Re: [PATCH v1] reset: Make optional stuff optional for all users

On Mon, 2017-04-03 at 17:09 +0200, Philipp Zabel wrote:
> On Mon, 2017-04-03 at 14:33 +0000, Shevchenko, Andriy wrote:
> > On Mon, 2017-04-03 at 17:31 +0300, Andy Shevchenko wrote:
> > > On Mon, 2017-04-03 at 16:27 +0200, Philipp Zabel wrote:
> > > > 
> > > > >  	int rstc_id;
> > > > >  	int ret;
> > > > >  
> > > > > -	if (!node)
> > > > > -		return ERR_PTR(-EINVAL);
> > > > > -
> > > > 
> > > > This should be
> > > > 
> > > > 	if (!node)
> > > > 		return optional ? NULL : ERR_PTR(-EINVAL);
> > > > 
> > > > instead. Can you confirm this works for Intel boards with DW
> > > > UART? I
> > > > can
> > > > fix it up when applying if you agree.
> > > 
> > > I don't think it worth to change. I specifically checked all of_*
> > > calls
> > > in that function and they cope pretty nice with node == NULL.
> 
> __of_reset_control_get called with id != NULL calls
> of_property_match_string first, which then returns -EINVAL if
> node == NULL, which makes __of_reset_control_get return NULL if
> optional
> or -ENOENT otherwise, even though the correct return value would be
> -EINVAL in the DT case.

Error handling mess as usual. :-)

> 
> __of_reset_control_get called with id == NULL calls
> of_parse_phandle_with_args first, which calls
> __of_parse_phandle_with_args, which returns an undefined value if
> np == NULL, as far as I can tell:
> of_for_each_phandle first calls of_phandle_iterator_init, which, when
> called with np == NULL clears the iterator structure returns -ENOENT.
> The return value is ignored in the of_for_each_phandle macro, and
> of_phandle_iterator_next is then called and returns -ENOENT because
> it->cur == NULL, ending the loop without ever assigning a value to rc.
> __of_parse_phandle_with_args then returns the uninitialized value.

It returns -ENOENT. Error value is kept in function variable rc.

> 
> The point being, instead of having to regularly forage through a
> number
> of of_ API functions to make sure my expectations are still met, I'd
> prefer to keep the check in place.

I would not insist, I already shared my view on this.

I really don't like ping-ponging of the code. Perhaps you would fix it
once for the best now?

> 
> > > 
> > > So, I rather to go with my initial change.
> > > 
> > 
> > Hit Enter before closing another thought.
> > 
> > When you come with solution where this __of_reset_control_get() will
> > be
> > called only for node != NULL case you will not need that check
> > either.
> 
> __of_reset_control_get is public API (via of_reset_control_get), so I
> can't guarantee node != NULL even in the DT case.

Yes, and that's why other callees will return some error codes there.

> 
> > So, I would go my solution because of two benefits:
> > - it fixes bug
> 
> True.
> 
> > - if will not bring ping-ponging code
> 
> Unfortunately not.

Fortunately yes, if someone will fix DT error code mess in the first
place.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy