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From: Arnd Bergmann <arnd@arndb.de>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	afzal mohammed <afzal.mohd.ma@gmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: ARM: static kernel in vmalloc space
Date: Thu, 30 Jul 2020 12:17:52 +0200	[thread overview]
Message-ID: <CAK8P3a3hWSROf9N8YthU_LHEgD3aKzJbemyyhoJ_jPTR4nn=EA@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdZ0YT7JoBdYHSb1bbZUv_ovjkBg7yx7gHbG5VjEDV8vhQ@mail.gmail.com>

On Thu, Jul 30, 2020 at 11:33 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> On Fri, May 15, 2020 at 5:41 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> [Russell]
> > > There are some aliasing VIPT implementations on ARMv6, but I don't
> > > remember how common.
> >
> > I thought it was only realview-pb and omap2, but it seems there
> > are more, at least ast2500 is an important example.
> >
> > I could not find information about integrator-cp and picoxcell.
> (...)
> >   integrator CM1136JF-S core module: arm1136r?, 16kb non-aliasing VIPT
> > ? integrator CTB36 core tile: arm1136r?, ???
>
> These do exist, the Integrators have pluggable CPU core modules.
> What you do is populate the core module slot on the Integrator CP
> with a CM1136.

Here the question is really what the cache size would be. 16kb
caches are non-aliasing, while 32kb caches would be aliasing.
The particular core revision would tell you whether this is an ARMv6
(1136r0) or ARMv6k (1136r1) implementation.

> That said, I think I am the only user of the Integrator/CP actual
> hardware. And I don't have this core module. So I think it will be
> safe to drop support for that specific VIPT implementation by the
> token that if a tree falls in the forest and noone
> is there to hear it, it does not make a sound.
>
> As for physically existing VIPT 1136/1176 systems the Ambarella
> legacy SoCs that are not upstream is the big consumer of these.
>
> Ambarella's main customer is GoPro cameras and similar
> products. I have no idea if they ever upgrade kernels on these
> things though, I think not, but it would be great if someone knows
> them and can ask whether this is a concern for them. (They
> should be working with the community IMO, but is one of those
> companies that for some reason do not.)

It seems unlikely that there is still enough interest in the old
GoPro chips.

Apparently GoPro Hero3+ from 2013 already used a Cortex-A9
based Ambarella chip, and according to Wikipedia in 2017 they
started making their own SoCs rather using Ambarella's.

I found some source code for both the arm11 version [1] and
the Cortex-A9 based chips, the last update on either of those
that was in 2016. The boot log in [2] shows this is a nonaliasing
cache btw.

Anyway, as I said earlier, as long as AST2500 (or OMAP2) is used,
aliasing dcaches remain a concern for ARMv6-enabled kernels.

     Arnd

[1] https://github.com/evilwombat/gopro-linux/tree/master/arch/arm/mach-ambarella
[2] https://www.tapatalk.com/groups/goprouser/hero3-black-firmware-studies-physical-teardown-pho-t10016-s10.html#p58148

      reply	other threads:[~2020-07-30 10:18 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-31  9:32 [PATCH 0/3] Highmem support for 32-bit RISC-V Eric Lin
2020-03-31  9:32 ` [PATCH 1/3] riscv/mm: Add pkmap region and CONFIG_HIGHMEM Eric Lin
2020-03-31  9:32 ` [PATCH 2/3] riscv/mm: Implement kmap() and kmap_atomic() Eric Lin
2020-03-31  9:32 ` [PATCH 3/3] riscv/mm: Add pkmap in print_vm_layout() Eric Lin
2020-04-02  9:31 ` [PATCH 0/3] Highmem support for 32-bit RISC-V Arnd Bergmann
2020-04-08  3:51   ` Alan Kao
2020-04-08 14:40     ` Arnd Bergmann
2020-04-14 15:17       ` afzal mohammed
2020-04-14 19:29         ` Arnd Bergmann
2020-04-15 13:54           ` afzal mohammed
2020-05-03 14:50             ` afzal mohammed
2020-05-03 20:20               ` Arnd Bergmann
2020-05-04  9:10                 ` afzal mohammed
2020-05-04 11:27                   ` Arnd Bergmann
2020-05-11 14:21                     ` ARM: static kernel in vmalloc space (was Re: [PATCH 0/3] Highmem support for 32-bit RISC-V) afzal mohammed
2020-05-11 15:29                       ` Arnd Bergmann
2020-05-12 10:47                         ` ARM: static kernel in vmalloc space afzal mohammed
2020-05-12 19:49                           ` Arnd Bergmann
2020-05-14 11:17                             ` afzal mohammed
2020-05-14 12:41                               ` Arnd Bergmann
2020-05-14 13:35                                 ` afzal mohammed
2020-05-14 14:44                                   ` afzal mohammed
2020-05-14 15:32                                   ` Arnd Bergmann
2020-05-16  6:06                                     ` afzal mohammed
2020-05-16  7:35                                       ` Arnd Bergmann
2020-06-07 12:59                                         ` ARM: vmsplit 4g/4g afzal mohammed
2020-06-07 16:11                                           ` Russell King - ARM Linux admin
2020-06-08 11:09                                             ` afzal mohammed
2020-06-10 10:10                                               ` Linus Walleij
2020-06-12 10:25                                                 ` afzal mohammed
2020-06-15  9:11                                                   ` Linus Walleij
2020-06-15 10:01                                                     ` afzal mohammed
2020-06-07 19:26                                           ` Arnd Bergmann
2020-06-08 11:18                                             ` afzal mohammed
2020-06-08 14:43                                               ` Arnd Bergmann
2020-06-08 15:17                                                 ` afzal mohammed
2020-06-09 12:15                                                   ` afzal mohammed
2020-06-09 14:22                                                     ` Arnd Bergmann
2020-05-14 16:25                                 ` ARM: static kernel in vmalloc space Russell King - ARM Linux admin
2020-05-14 21:12                                   ` Arnd Bergmann
2020-05-14 23:40                                     ` Russell King - ARM Linux admin
2020-05-15 15:41                                       ` Arnd Bergmann
2020-07-30  9:33                                         ` Linus Walleij
2020-07-30 10:17                                           ` Arnd Bergmann [this message]

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