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

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Message-ID: <20170804150825.GE29306@minitux>
Date:   Fri, 4 Aug 2017 08:08:25 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Rob Herring <robh+dt@...nel.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 Fri 04 Aug 07:50 PDT 2017, Rob Herring wrote:

> 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.
> 

The problem is that the fdt_node of the reserved_mem is the offset in
the flat tree, but we don't carry this information with us when we
create the individual device_nodes.

So, AFAICT, to fill out this information at any point after returning
from the particular populate_node() call we will have to use some sort
of heuristics in matching the two nodes.

> > 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.
> 

I'll update patch 1/5 and resend the series.

Thanks,
Bjorn