linux-kernel - Re: [PATCH v2 5/5] lib/cpumask: add FORCE_NR

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Date:   Tue, 18 Oct 2022 15:41:10 +0200
From:   Andreas Schwab <schwab@...e.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Sander Vanheule <sander@...nheule.net>,
        Alexey Klimov <klimov.linux@...il.com>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v2 5/5] lib/cpumask: add FORCE_NR_CPUS config option

On Okt 18 2022, Geert Uytterhoeven wrote:

> Moreover, this cannot be used on all systems.  E.g. on Icicle Kit with
> Microchip PolarFire SoC, CONFIG_NR_CPUS needs to be larger than 4,
> as the system has actually 5 CPU cores (1xE51 and 4xU54), but Linux
> runs only on 4 of them.  So you cannot use FORCE_NR_CPUS=y.

But does Linux acually see the E51 core?  On the Hifive boards it is
disabled in the device tree, and the cpu probing just skips it,
effectively resulting in only four cpus.

-- 
Andreas Schwab, SUSE Labs, schwab@...e.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."