linux-kernel - Re: [PATCH] MIPS: add support for buggy MT7621S core detection

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Date:   Wed, 7 Apr 2021 11:49:53 -0700
From:   Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Wei Li <liwei391@...wei.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        linux-mips@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Felix Fietkau <nbd@....name>
Subject: Re: [PATCH] MIPS: add support for buggy MT7621S core detection

On Wed, Apr 7, 2021 at 6:49 AM Maciej W. Rozycki <macro@...am.me.uk> wrote:
>
> On Mon, 5 Apr 2021, Ilya Lipnitskiy wrote:
>
> > Thanks for the comments. Including asm/bugs.h in asm/mips-cps.h led to
> > some circular dependencies when I tried it, but I will try again based
> > on your feedback - indeed it would be much cleaner to have this logic
> > in mips_cps_numcores. The only wrinkle is that mips_cps_numcores may
> > return a different value on MT7621 after the cores have started due to
> > CPULAUNCH flags changing, but nobody calls mips_cps_numcores later
> > anyway, so it's a moot point today. I will clean up the change and
> > resend.
>
>  Hmm, I don't know this system, but by the look of the code it queries
> launch[2], which I gather refers to the VPE #0 of an inexistent core #1,
> so why would the structure change given that there is no corresponding
> silicon?
The structure would change only on the dual-core flavor of MT7621, the
single-core would always report 1 core, but on the dual-core, if
somebody were to call mips_cps_numcores after the second core had
already started, mips_cps_numcores would return 1 instead of 2. I
think it may be feasible to fix it by checking other flags, but there
is no use case for that today, so I'd rather keep this hacky logic to
a minimum.

Ilya