linux-kernel - Re: [PATCH v4 09/14] of: reserved-memory: Fix using wrong number of cells to get property 'alignment'

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Message-ID: <CAL_Jsq+P=sZu6Wnqq7uEnGMnAQGNEDf_B+VgO8E8ob4RX8b=QA@mail.gmail.com>
Date: Wed, 26 Feb 2025 15:30:36 -0600
From: Rob Herring <robh@...nel.org>
To: Zijun Hu <zijun_hu@...oud.com>
Cc: William McVicker <willmcvicker@...gle.com>, Zijun Hu <quic_zijuhu@...cinc.com>, 
	Saravana Kannan <saravanak@...gle.com>, Maxime Ripard <mripard@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Grant Likely <grant.likely@...retlab.ca>, 
	Marc Zyngier <maz@...nel.org>, Andreas Herrmann <andreas.herrmann@...xeda.com>, 
	Marek Szyprowski <m.szyprowski@...sung.com>, Catalin Marinas <catalin.marinas@....com>, 
	Mike Rapoport <rppt@...nel.org>, Oreoluwa Babatunde <quic_obabatun@...cinc.com>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v4 09/14] of: reserved-memory: Fix using wrong number of
 cells to get property 'alignment'

On Wed, Feb 26, 2025 at 2:31 PM Zijun Hu <zijun_hu@...oud.com> wrote:
>
> On 2025/2/27 03:45, Rob Herring wrote:
> >> Right, I think it's already backported to the LTS kernels, but if it breaks any
> >> in-tree users then we'd have to revert it. I just like Rob's idea to instead
> >> change the spec for obvious reasons 🙂
> > While if it is downstream, it doesn't exist, I'm reverting this for now.
>
> perhaps, it is better for us to slow down here.
>
> 1) This change does not break any upstream code.
>    is there downstream code which is publicly visible and is broken by
>    this change ?

We don't know that unless you tested every dts file. We only know that
no one has reported an issue yet.

Even if we did test everything, there are DT's that aren't in the
kernel tree. It's not like this downstream DT is using some
undocumented binding or questionable things. It's a standard binding.

Every time this code is touched, it breaks. This is not even the only
breakage right now[1].

> 2) IMO, the spec may be right.
>    The type of size is enough to express any alignment wanted.
>    For several kernel allocators. type of 'alignment' should be the type
>    of 'size', NOT the type of 'address'

As I said previously, it can be argued either way.

Rob

[1] https://lore.kernel.org/all/20250226115044.zw44p5dxlhy5eoni@pengutronix.de/