linux-kernel - Re: [PATCH 1/3] of: base: add support to get machine compatible string

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Message-ID: <ae92e013-b41b-6caa-b32f-284ffb6f5aa0@ti.com>
Date:   Wed, 23 Nov 2016 13:19:47 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Sudeep Holla <sudeep.holla@....com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Russell King <linux@...linux.org.uk>
CC:     LKML <linux-kernel@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        linux-drm <dri-devel@...ts.freedesktop.org>,
        linux-devicetree <devicetree@...r.kernel.org>,
        Jyri Sarha <jsarha@...com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        David Airlie <airlied@...ux.ie>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 1/3] of: base: add support to get machine compatible
 string

On Tuesday 22 November 2016 09:16 PM, Sudeep Holla wrote:
> Hi Sekhar,
> 
> On 22/11/16 15:06, Sekhar Nori wrote:
>> Hi Sudeep,
>>
>> On Tuesday 22 November 2016 04:23 PM, Sudeep Holla wrote:
>>>
>>>
>>> On 22/11/16 10:41, Bartosz Golaszewski wrote:
>>>> Add a function allowing to retrieve the compatible string of the root
>>>> node of the device tree.
>>>>
>>>
>>> Rob has queued [1] and it's in -next today. You can reuse that if you
>>> are planning to target this for v4.11 or just use open coding in your
>>> driver for v4.10 and target this move for v4.11 to avoid cross tree
>>> dependencies as I already mentioned in your previous thread.
>>
>> I dont have your original patch in my mailbox, but I wonder if
>> returning a pointer to property string for a node whose reference has
>> already been released is safe to do? Probably not an issue for the root
>> node, but still feels counter-intuitive.
>>
> 
> I am not sure if I understand the issue here. Are you referring a case
> where of_root is freed ?

Yes, right, thats what I was hinting at. Since you are giving up the
reference to the device node before the function returns, the user can
be left with a dangling reference.

> Also I have seen drivers today just using this pointer directly, but
> it's better to copy the string(I just saw this done in one case)

Hmm, the reference is given up before the API returns, so I doubt
copying it later is any additional benefit.

I suspect this is a theoretical issue though since root device node is
probably never freed.

Thanks,
Sekhar