linux-kernel - Re: [RFC PATCH v2 2/6] of: reserved_mem: Swicth call to unflatten_device_tree() to after paging

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Date:   Sun, 10 Dec 2023 16:51:56 -0800
From:   Oreoluwa Babatunde <quic_obabatun@...cinc.com>
To:     Rob Herring <robh@...nel.org>
CC:     <catalin.marinas@....com>, <will@...nel.org>,
        <frowand.list@...il.com>, <dinguyen@...nel.org>,
        <chenhuacai@...nel.org>, <tsbogend@...ha.franken.de>,
        <jonas@...thpole.se>, <stefan.kristiansson@...nalahti.fi>,
        <shorne@...il.com>, <mpe@...erman.id.au>,
        <ysato@...rs.sourceforge.jp>, <dalias@...c.org>,
        <glaubitz@...sik.fu-berlin.de>, <richard@....at>,
        <anton.ivanov@...bridgegreys.com>, <johannes@...solutions.net>,
        <chris@...kel.net>, <jcmvbkbc@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <kernel@...cinc.com>
Subject: Re: [RFC PATCH v2 2/6] of: reserved_mem: Swicth call to
 unflatten_device_tree() to after paging_init()

On 12/6/2023 1:31 PM, Rob Herring wrote:
> On Mon, Dec 04, 2023 at 10:54:05AM -0800, Oreoluwa Babatunde wrote:
>> Switch call to unflatten_device_tree() to after paging_init() on other
>> archs to follow new order in which the reserved_mem regions are
>> processed.
> You did this so that you could allocate memory for the reserved regions. 
> But unflatten_device_tree() can already do allocations using memblock. 
> So the same thing should work for you.
>
> I suspect that moving this will break any arch that called an of_* API 
> between the original call and the new call location.
>
> Rob
Hi Rob,

Thank you for your feedback. You are correct, I see that
unflatten_device_tree() is allocating memory from memblock and writing
to it before paging_init() is called on these other architectures.

This series will still require fdt_init_reserved_mem() to be called
after paging_init() on architectures such as arm64 which require
paging_init() to run before memblock allocated memory is writable.

In light of this, there seems to be no non-architecture-specific
universal calling point to stick in fdt_init_reserved_mem() that works
for all architectures.  Therefore, I propose taking out the call to
fdt_init_reserved_mem() from the unflatten_device_tree() function and
placing it in the setup_arch() function for each architecture.
(similar to the way it was in v1 of this series).

Doing this will allow us to place  fdt_init_reserved_mem() after
paging_init() on architectures that require paging_init() to be called
before memblock allocated memory is writable, and place it before
paging_init() on architectures that does not require paging_init() to be
called before writing to memblock allocated memory.

fdt_init_reserved_mem() can also be called after unflatten_device_tree()
on all architectures to ensure we get the speed benefits of using the
unflattened device tree APIs for the final pass.

Regards,
Oreoluwa