linux-kernel - Re: [PATCH 5/7] powerpc/85xx: p2020: Define just one machine description

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Date:   Mon, 26 Sep 2022 12:08:56 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Scott Wood <oss@...error.net>, Sinan Akman <sinan@...teme.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/7] powerpc/85xx: p2020: Define just one machine
 description

On Monday 26 September 2022 10:02:47 Christophe Leroy wrote:
> > +static int __init p2020_probe(void)
> >   {
> > -	if (of_machine_is_compatible("fsl,P2020RDB-PC"))
> > -		return 1;
> > -	return 0;
> > +	struct device_node *p2020_cpu;
> > +
> > +	/*
> > +	 * There is no common compatible string for all P2020 boards.
> > +	 * The only common thing is "PowerPC,P2020@0" cpu node.
> > +	 * So check for P2020 board via this cpu node.
> > +	 */
> > +	p2020_cpu = of_find_node_by_path("/cpus/PowerPC,P2020@0");
> > +	if (!p2020_cpu)
> > +		return 0;
> 
> This looks odd. I though all probe were using the compatible, and in 
> fact I have a series in preparation that drops all 
> of_machine_is_compatible() checks in probe functions and do it in the 
> caller instead, after adding a .compatible string in the machine 
> description.
> 
> Is there really no compatible that can be used for all p2020 ?

Really. There is none. I have looked into all available P2020 DTB files
(either externals passed by bootloader or kernel in-tree) and there is
no common compatible string. The only "common" thing is cpu node, how I
implemented it int this patch series.

And same issue is with boards with P101x and P102x DTB files.