linux-kernel - Re: [PATCH v2 2/5] of: reserved_mem: Accessor for acquiring reserved

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Date:   Fri, 4 Aug 2017 09:50:55 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-soc@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] of: reserved_mem: Accessor for acquiring reserved_mem

On Thu, Aug 3, 2017 at 6:31 PM, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
> On Thu 03 Aug 10:45 PDT 2017, Rob Herring wrote:
>
>> On Wed, Aug 2, 2017 at 9:57 PM, Bjorn Andersson
>> <bjorn.andersson@...aro.org> wrote:
>> > In some cases drivers referencing a reserved-memory region might want to
>> > remap the entire region, but when defining the reserved-memory by "size"
>> > the client driver has no means to know the associated base address of
>> > the reserved memory region.
>> >
>> > This patch adds an accessor for such drivers to acquire a handle to
>> > their associated reserved-memory for this purpose.
>> >
>> > A complicating factor for the implementation is that the reserved_mem
>> > objects are created from the flattened DeviceTree, as such we can't
>> > use the device_node address for comparison. Fortunately the name of the
>> > node will be used as "name" of the reserved_mem and will be used when
>> > building the full_name, so we can compare the "name" with the basename
>> > of the full_name to find the match.
>>
>> Maybe we should add the device_node pointer when we unflatten?
>>
>
> It did try to figure something sane out in that direction.
>
> The solution I came up with was to amend populate_node() to in a !dryrun
> block check if the "dad" full_name is /reserved-memory and if so
> call call a new accessor in of_reserved_mem.c to add the "np" to the
> reserved_mem object with fdt_node equal offset.

I was thinking doing it with the unflattened tree just after it has
been unflattened rather than during unflattening.

> This code path is already cluttered due to the version differences when
> it comes to building full_name and we would end up checking for each
> node in the entire tree if the parent happens to be "/reserved-mem".
>
> So I went for the less intrusive and more straight forward comparison
> with basename(full_name) instead.

That's good, because full_name is about to become just the basename.

Rob