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Message-ID: <6a288c4f54aa501e265a4f4847f2d2e53c597c34.camel@gmail.com>
Subject: Re: [PATCH] of: fdt: Honor CONFIG_CMDLINE* even without /chosen node
From:   Alexander Sverdlin <alexander.sverdlin@gmail.com>
To:     Rob Herring <robh@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>
Cc:     devicetree@vger.kernel.org, Frank Rowand <frowand.list@gmail.com>,
        linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@kernel.org>,
        Nikita Shubin <nikita.shubin@maquefel.me>,
        Hartley Sweeten <hsweeten@visionengravers.com>,
        Lukasz Majewski <lukma@denx.de>,
        Linus Walleij <linusw@kernel.org>
Date:   Tue, 13 Dec 2022 23:07:44 +0100
In-Reply-To: <20221213152920.GA1025576-robh@kernel.org>
References: <11af73e05bad75e4ef49067515e3214f6d944b3d.camel@gmail.com>
         <CACRpkdaXxPE3XhPnprhJ7GGjn9X_GMsCJ3mn26P90GcHzhsQDg@mail.gmail.com>
         <20221213152920.GA1025576-robh@kernel.org>
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Hello Rob,

On Tue, 2022-12-13 at 09:29 -0600, Rob Herring wrote:
> On Tue, Dec 13, 2022 at 09:51:33AM +0100, Linus Walleij wrote:
> > On Mon, Dec 12, 2022 at 7:01 AM Alexander Sverdlin
> > <alexander.sverdlin@gmail.com> wrote:
> >=20
> > > I do not read a strict requirement on /chosen node in either ePAPR or=
 in
> > > Documentation/devicetree. Help text for CONFIG_CMDLINE and
> > > CONFIG_CMDLINE_EXTEND doesn't make their behavior explicitly dependen=
t on
> > > the presence of /chosen or the presense of /chosen/bootargs.
> > >=20
> > > However the early check for /chosen and bailing out in
> > > early_init_dt_scan_chosen() skips CONFIG_CMDLINE handling which is no=
t
> > > really related to /chosen node or the particular method of passing cm=
dline
> > > from bootloader.
> > >=20
> > > This leads to counterintuitive combinations (assuming
> > > CONFIG_CMDLINE_EXTEND=3Dy):
> > >=20
> > > a) bootargs=3D"foo", CONFIG_CMDLINE=3D"bar" =3D> cmdline=3D=3D"foo ba=
r"
> > > b) /chosen missing, CONFIG_CMDLINE=3D"bar" =3D> cmdline=3D=3D""
> > > c) bootargs=3D"", CONFIG_CMDLINE=3D"bar" =3D> cmdline=3D=3D" bar"
> > >=20
> > > Move CONFIG_CMDLINE handling outside of early_init_dt_scan_chosen() s=
o that
> > > cases b and c above result in the same cmdline.
> > >=20
> > > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
> >=20
> > Excellent debugging Alexander!
> > Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> >=20
> > I also think this should go to stable.
>=20
> We have to be careful there. This could change behavior on a working=20
> system. A system taking the cmdline entirely from a built kernel and=20
> no initrd is going to be pretty customized already, I think they can=20
> carry a patch. What platform is this anyways?

I've stumbled upon this testing first DT conversion patches for EP93xx (ARM=
).

> This has actually been known for some time[1][2]. My concern in the past=
=20
> (besides wanting all the cmdline manipulation being common) was MIPS.=20

This "change of behavior" actually changes one exact corner case:
no /chosen node + CONFIG_CMDLINE!=3D"" + CONFIG_CMDLINE_EXTEND=3Dy

If someone was intentionally hiding something in the config file
under CONFIG_CMDLINE but didn't want it to appear on the kernel command
line in the past, he could just reconfigure new kernel version after
the change and remove the above configs.

> MIPS in particular has lots of sources for cmdline and ways to combine=
=20
> it. However, MIPS has since stopped using this code and does their own=
=20
> parsing (not great either IMO).

I agree, this code screams to be common.

--=20
Alexander Sverdlin.