linux-kernel - Re: [PATCH 2/8] CMDLINE: drivers: of: ifdef out cmdline section

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Message-ID: <20210409012657.GH3981976@zorba>
Date:   Thu, 8 Apr 2021 18:26:57 -0700
From:   Daniel Walker <danielwa@...co.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Daniel Gimpelevich <daniel@...pelevich.san-francisco.ca.us>,
        Andrew Morton <akpm@...ux-foundation.org>,
        X86 ML <x86@...nel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Frank Rowand <frowand.list@...il.com>,
        xe-linux-external@...co.com,
        Ruslan Ruslichenko <rruslich@...co.com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/8] CMDLINE: drivers: of: ifdef out cmdline section

On Wed, Apr 07, 2021 at 05:59:15PM -0500, Rob Herring wrote:
> On Tue, Mar 30, 2021 at 04:17:53PM -0700, Daniel Walker wrote:
> > On Tue, Mar 30, 2021 at 02:49:13PM -0500, Rob Herring wrote:
> > > On Tue, Mar 30, 2021 at 12:57 PM Daniel Walker <danielwa@...co.com> wrote:
> > > >
> > > > It looks like there's some seepage of cmdline stuff into
> > > > the generic device tree code. This conflicts with the
> > > > generic cmdline implementation so I remove it in the case
> > > > when that's enabled.
> > > >
> > > > Cc: xe-linux-external@...co.com
> > > > Signed-off-by: Ruslan Ruslichenko <rruslich@...co.com>
> > > > Signed-off-by: Daniel Walker <danielwa@...co.com>
> > > > ---
> > > >  drivers/of/fdt.c | 14 ++++++++++++++
> > > >  1 file changed, 14 insertions(+)
> > > >
> > > > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > > > index dcc1dd96911a..d8805cd9717a 100644
> > > > --- a/drivers/of/fdt.c
> > > > +++ b/drivers/of/fdt.c
> > > > @@ -25,6 +25,7 @@
> > > >  #include <linux/serial_core.h>
> > > >  #include <linux/sysfs.h>
> > > >  #include <linux/random.h>
> > > > +#include <linux/cmdline.h>
> > > >
> > > >  #include <asm/setup.h>  /* for COMMAND_LINE_SIZE */
> > > >  #include <asm/page.h>
> > > > @@ -1050,6 +1051,18 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
> > > >
> > > >         /* Retrieve command line */
> > > >         p = of_get_flat_dt_prop(node, "bootargs", &l);
> > > > +
> > > > +#if defined(CONFIG_GENERIC_CMDLINE) && defined(CONFIG_GENERIC_CMDLINE_OF)
> > > 
> > > Moving in the wrong direction... This code already has too many
> > > #ifdef's. I like Christophe's version as it gets rid of all the code
> > > here.
> >  
> > It's temporary .. Notice CONFIG_GENERIC_CMDLINE_OF is only used on PowerPC. I
> > experienced doubling on arm64 when this was used (i.e. the append and prepend
> > was added twice).
> > 
> > I don't think there are any other users which can't be moved outside the device
> > tree code, but powerpc uses this function three times during boot up plus the
> > prom_init user. It's possible to use the generic command line in all four places,
> > but it become space inefficient.
> 
> What's the 3rd use? I count kaslr code and in 
> early_init_dt_scan_chosen_ppc. Do we need to build the command line for 
> kaslr seed? Getting any build time value from the kernel is pointless.

I think I may have been mistaken. I added a dump_stack() , but there may have
been other stack traces during bootup on prior -rcX's I was testing.

I re-ran the test and I only see one user on powerpc and powerpc64,

powerpc64,

[    T0] Call Trace:
[    T0] [c000000001517d00] [c00000000077e910] dump_stack+0xc4/0x114 (unreliable)
[    T0] [c000000001517d50] [c000000001186fb4] early_init_dt_scan_chosen+0x238/0x324
[    T0] [c000000001517de0] [c000000001138b00] early_init_dt_scan_chosen_ppc+0x20/0x194
[    T0] [c000000001517e10] [c000000001186ae0] of_scan_flat_dt+0xc8/0x130
[    T0] [c000000001517e70] [c000000001139404] early_init_devtree+0xa4/0x48c
[    T0] [c000000001517f10] [c00000000113ac90] early_setup+0xc8/0x254
[    T0] [c000000001517f90] [000000000000c754] 0xc754

powerpc32,

Call Trace:
[c06bbee0] [c067e334] early_init_dt_scan_chosen+0xf8/0x1dc (unreliable)
[c06bbf10] [c0666ec4] early_init_dt_scan_chosen_ppc+0x18/0x6c
[c06bbf30] [c067e048] of_scan_flat_dt+0x98/0xf4
[c06bbf70] [c0667234] early_init_devtree+0x48/0x2d0
[c06bbfb0] [c06679cc] machine_init+0x98/0xcc
[c06bbff0] [c0000398] set_ivor+0x114/0x154

I think it would be possible to just move the generic handling entire into
architecture code.

Daniel