linux-kernel - Re: [PATCH] ARM: cacheinfo fix format field mask

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Message-ID: <CAA8EJprB9tBoqUaZKnGrJQVPpRA86ynB6k42dOCW7HG-VTfhbA@mail.gmail.com>
Date: Tue, 21 Jan 2025 16:52:11 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>, Linus Walleij <linus.walleij@...aro.org>, 
	Sudeep Holla <sudeep.holla@....com>, Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH] ARM: cacheinfo fix format field mask

On Tue, 21 Jan 2025 at 16:19, Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> On Tue, Jan 21, 2025 at 03:12:13PM +0100, Geert Uytterhoeven wrote:
> > Hi Dmitry,
> >
> > Thanks for your patch!
> >
> > On Wed, Jan 15, 2025 at 12:11 PM Dmitry Baryshkov
> > <dmitry.baryshkov@...aro.org> wrote:
> > > Fix C&P error left unnoticed during the reviews. The FORMAT field spans
> > > over bits 29-31, not 24-27 of the CTR register.
> >
> > Please add
> >
> >     This causes a warning on e.g. Cortex-A8 and Cortex-A9:
> >
> >         WARNING: CPU: 0 PID: 0 at arch/arm/kernel/cacheinfo.c:43
> > cache_line_size+0x84/0x94
> >
> > so people find this patch when looking up the warning.
> >
> > > Fixes: a9ff94477836 ("ARM: 9433/2: implement cacheinfo support")
> > > Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > > Closes: https://lore.kernel.org/linux-arm-msm/01515ea0-c6f0-479f-9da5-764d9ee79ed6@samsung.com/
> > > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> >
> > This fixes the warning on Cortex-A8/A9, so
> > Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> >
> > Note that this changes HWalign on Cortex-A9 (various Renesas SoCs,
> > with 1, 2, or 4 CPU cores):
> >
> >     -SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=<N>, Nodes=1
> >     +SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=<N>, Nodes=1
> >
> > On Cortex-A8 (BeagleBone Black, i.e. AM335x), it changes HWalign,
> > and causes a warning message:
> >
> >     -SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
> >     +SLUB: HWalign=16, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
> >      ...
> >     +cacheinfo: Unable to detect cache hierarchy for CPU 0
> >
>
> Also, has this been tested on CPUs that don't implement the cache type
> register?

It returns -EOPNOTSUPP for anything <= v7 (or those v7-but-really-v6).
And those CPUs are required to implement the register.

>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!



-- 
With best wishes
Dmitry