linux-kernel - Re: [PATCH 1/3] Input: twl4030-vibra: fix sibling-node lookup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 13 Nov 2017 09:11:44 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable <stable@...r.kernel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Marek Belisko <marek@...delico.com>,
        Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH 1/3] Input: twl4030-vibra: fix sibling-node lookup

On Sun, 12 Nov 2017, Johan Hovold wrote:

> [ +CC: Lee, Rob and device-tree list ]
> 
> On Sat, Nov 11, 2017 at 09:50:59AM -0800, Dmitry Torokhov wrote:
> > On Sat, Nov 11, 2017 at 04:43:37PM +0100, Johan Hovold wrote:
> > > A helper purported to look up a child node based on its name was using
> > > the wrong of-helper and ended up prematurely freeing the parent of-node
> > > while searching the whole device tree depth-first starting at the parent
> > > node.
> > 
> > Ugh, this all is pretty ugly business. Can we teach MFD to allow
> > specifying firmware node to be attached to the platform devices it
> > creates in mfd_add_device() so that the leaf drivers simply call
> > device_property_read_XXX() on their own device and not be bothered with
> > weird OF refcount issues or what node they need to locate and parse?

If a child compatible is provided, we already set the child's
of_node.  It's then up to the driver (set) author(s) to use it in the
correct manner. 

> Yeah, that may have helped. You can actually specify a compatible string
> in struct mfd_cell today which does make mfd_add_device() associate a
> matching child node.
> 
> Some best practice regarding how to deal with MFD and device tree would
> be good to determine and document too. For example, when should
> of_platform_populate() be used in favour of mfd_add_device()?

When the device supports DT and its entire hierarchical layout, along
with all of its attributes can be expressed in DT.

> And how best to deal with sibling nodes, which is part of the problem
> here (I think the mfd should have provided a flag rather than having
> subdrivers deal with sibling nodes, for example).

I disagree.  The only properties the MFD (parent) driver is interested
in is ones which are shared across multiple child devices.
*Everything* which pertains to only a single child device should be
handled by its accompanying driver. 

> That said, driver authors using the wrong of-helper could possibly have
> been avoided by amending the kernel docs (I'll do that as a follow up),
> but once these incorrect usages get in, only review can prevent them
> from being reproduced through copy-paste coding.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog