Re: [PATCH v2] of/fdt: Rework early_init_dt_scan_memory() to call directly

From: Rob Herring <robh@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: John Crispin <john@phrozen.org>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Frank Rowand <frowand.list@gmail.com>,
	"open list:MIPS" <linux-mips@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	devicetree@vger.kernel.org
Subject: Re: [PATCH v2] of/fdt: Rework early_init_dt_scan_memory() to call directly
Date: Tue, 14 Dec 2021 08:40:02 -0600	[thread overview]
Message-ID: <CAL_JsqKbaRgivZMxEj6Mjdny2LNeSA1GQyDW-nQe7E2irPc-Fw@mail.gmail.com> (raw)
In-Reply-To: <877dc7mo3o.fsf@mpe.ellerman.id.au>

On Tue, Dec 14, 2021 at 5:18 AM Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Rob Herring <robh@kernel.org> writes:
> > On Mon, Dec 13, 2021 at 6:47 AM Michael Ellerman <mpe@ellerman.id.au> wrote:
> >> Rob Herring <robh@kernel.org> writes:
> >> > Use of the of_scan_flat_dt() function predates libfdt and is discouraged
> >> > as libfdt provides a nicer set of APIs. Rework
> >> > early_init_dt_scan_memory() to be called directly and use libfdt.
> >> ...
> >> > diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> >> > index 6e1a106f02eb..63762a3b75e8 100644
> >> > --- a/arch/powerpc/kernel/prom.c
> >> > +++ b/arch/powerpc/kernel/prom.c
> >> > @@ -532,19 +532,19 @@ static int  __init early_init_drmem_lmb(struct drmem_lmb *lmb,
> >> >  }
> >> >  #endif /* CONFIG_PPC_PSERIES */
> >> >
> >> > -static int __init early_init_dt_scan_memory_ppc(unsigned long node,
> >> > -                                             const char *uname,
> >> > -                                             int depth, void *data)
> >> > +static int __init early_init_dt_scan_memory_ppc(void)
> >> >  {
> >> >  #ifdef CONFIG_PPC_PSERIES
> >> > -     if (depth == 1 &&
> >> > -         strcmp(uname, "ibm,dynamic-reconfiguration-memory") == 0) {
> >> > +     const void *fdt = initial_boot_params;
> >> > +     int node = fdt_path_offset(fdt, "/ibm,dynamic-reconfiguration-memory");
> >> > +
> >> > +     if (node > 0) {
> >> >               walk_drmem_lmbs_early(node, NULL, early_init_drmem_lmb);
> >> >               return 0;
> >> >       }
>
> It's that return that is the problem.
>
> Now that early_init_dt_scan_memory_ppc() is only called once, that
> return causes us to skip scanning regular memory nodes if there is an
> "ibm,dynamic-reconfiguration-memory" property present.
>
> So the fix is just:
>
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index 1098de3b172f..125661e5fcf3 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -538,10 +538,8 @@ static int __init early_init_dt_scan_memory_ppc(void)
>         const void *fdt = initial_boot_params;
>         int node = fdt_path_offset(fdt, "/ibm,dynamic-reconfiguration-memory");
>
> -       if (node > 0) {
> +       if (node > 0)
>                 walk_drmem_lmbs_early(node, NULL, early_init_drmem_lmb);
> -               return 0;
> -       }
>  #endif
>
>         return early_init_dt_scan_memory();

Thanks! I've rolled that in.

> > The only thing I see is now there is an assumption that 'memory' nodes
> > are off the root node only. Before they could be anywhere.
>
> I don't know of any machines where that would be a problem. But given
> all the wild and wonderful device trees out there, who really knows :)
>
> Maybe we should continue to allow memory nodes to be anywhere, and print
> a warning for any that aren't at the root. Then if no one reports any
> hits for the warning we could switch to only allowing them at the root?

I really doubt there's any case. I just have the least visibility into
what IBM DTs look like. I checked some old DT files I have and also
u-boot only supports off the root node.

Rob