linux-kernel - Re: ARM: OMAP2+: Grab reference to device nodes where needed

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Message-ID: <20170228172637.GA13455@roeck-us.net>
Date:   Tue, 28 Feb 2017 09:26:37 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Paul Walmsley <paul@...an.com>, Rob Herring <robh@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, Qi Hou <qi.hou@...driver.com>,
        linux-omap@...r.kernel.org, Peter Rosin <peda@...ntia.se>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: ARM: OMAP2+: Grab reference to device nodes where needed

On Tue, Feb 28, 2017 at 08:23:16AM -0800, Tony Lindgren wrote:
> * Guenter Roeck <linux@...ck-us.net> [170227 15:36]:
> > ping ... this problem is now seen in mainline.
> 
> Oops sorry I had accidentally tagged this with "next" instead of
> "fixes".
> 
> Looking at the patch though, can't we make of_node_get/put local to
> omap3xxx_hwmod_is_hs_ip_block_usable()?
> 
Not really.

Strictly speaking the patch fixes two problems:
1) of_find_node_by_name() gets a reference on "bus", thus of_node_put()
   is necessary to release it. This is the change in omap3xxx_hwmod_init().
2) of_find_node_by_name() drops a reference to the passed device node,
   thus it is necessary to call of_node_get(bus) in
   omap3xxx_hwmod_is_hs_ip_block_usable().

I should have stated that more clearly in the description.

We could ignore 1) to get rid of the warning, but that would leave us with
a dangling reference to the bus node. I could also improve the description,
or split the patch in two. Let me know what you prefer.

Another possible change would be to use of_get_child_by_name() instead of
of_find_node_by_name(). That would, however, only search immediate children
of the 'ocp' node, not all nodes. I  think that is what is actually intended
here, but I am not entirely sure. Thoughts ?

Either case, turns out I'll have to re-submit the patch because, as mentioned
above, of_find_node_by_name() gets a reference to the device node it returns,
so a put on that node is necessary in omap3xxx_hwmod_is_hs_ip_block_usable().

Guenter