Date:   Fri, 10 Mar 2023 18:20:51 +0300
From:   Dmitry Rokosov <ddrokosov@sberdevices.ru>
To:     Kevin Hilman <khilman@baylibre.com>
CC:     Arnd Bergmann <arnd@arndb.de>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Alexey Romanov <avromanov@sberdevices.ru>,
        Rob Herring <robh+dt@kernel.org>,
        <krzysztof.kozlowski+dt@linaro.org>, <jbrunet@baylibre.com>,
        <martin.blumenstingl@googlemail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        <devicetree@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-amlogic@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <kernel@sberdevices.ru>
Subject: Re: [PATCH v1 0/3] Meson A1 32-bit support
Message-ID: <20230310152051.ilz4qsgp3rplt4ad@CAB-WSD-L081021>
References: <8e5f9bfa-d612-cd43-d722-d04c40938c62@linaro.org>
 <20230227142809.kujmrraf3pcdhqyn@CAB-WSD-L081021>
 <f3e42012-609c-4085-b4f4-bd32bfc34aff@app.fastmail.com>
 <20230227155100.hhl4yvkyfqfyoa6h@CAB-WSD-L081021>
 <a5fa8b23-4ec8-475f-be5e-538b53d6f82d@app.fastmail.com>
 <33b58877-5167-c453-e686-1d10cdca66c0@linaro.org>
 <20230227165049.4y7jx5nnnlibe6kg@CAB-WSD-L081021>
 <7d29f3fd-b8c8-4687-b6a0-b8956dd39f0b@app.fastmail.com>
 <20230228084952.mgx3d3nw65yo5ebu@CAB-WSD-L081021>
 <7hedpxwq1i.fsf@baylibre.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <7hedpxwq1i.fsf@baylibre.com>
User-Agent: NeoMutt/20220415
Precedence: bulk

Hello Kevin,

On Thu, Mar 09, 2023 at 01:52:41PM -0800, Kevin Hilman wrote:
> Dmitry Rokosov <ddrokosov@sberdevices.ru> writes:
> 
> > On Mon, Feb 27, 2023 at 07:19:38PM +0100, Arnd Bergmann wrote:
> >> On Mon, Feb 27, 2023, at 17:50, Dmitry Rokosov wrote:
> >> > On Mon, Feb 27, 2023 at 05:38:49PM +0100, Neil Armstrong wrote:
> >> >> On 27/02/2023 17:15, Arnd Bergmann wrote:
> >> >> > On Mon, Feb 27, 2023, at 16:51, Dmitry Rokosov wrote:
> >> >> > 
> >> >> > Most of these don't apply in userspace, so the incentive to
> >> >> > run smaller 32-bit userland on systems with less than 1GB of
> >> >> > RAM usually outweighs the benefits of 64-bit userspace.
> >> >> 
> >> >> Thanks for the details!
> >> >
> >> > Looks like Thomas has already prepared a basic patch series for buildroot,
> >> > but maintainers declined it.
> >> >
> >> > https://lore.kernel.org/all/20220730194331.GA2515056@scaer/
> >> 
> >> I see. I know very little about buildroot, but it sounds like
> >> there are other ways of doing the same thing here. In general,
> >> this is pretty much an Arm specific problem. While you clearly
> >> want compat mode for small userland on any architecture but don't
> >> want 32-bit kernels, arm is the only one that has a different
> >> kernel "ARCH=" value and needs a separate gcc toolchain.
> >> 
> >> If the problem is only the toolchain, an easy way out may
> >> be to use clang instead of gcc as your compiler, as a single
> >> clang binary can target both 32-bit userland and 64-bit kernel
> >> on all supported architectures.
> >
> > Agreed with you. We will try different local approaches to support
> > compat build configurations. For now, prebuilt toolchain (buildroot make
> > sdk goal) is best way from my point of view. Anyway, we will try to
> > solve this problem in the our sandbox and stay on the 64-bit kernel.
> > Thank you for all the helpful details you shared, appreciate it!
> 
> Just to clarify one thing...
> 
> More specifically, this is a buildroot *build system* problem.  If you
> build the kernel separately from the rootfs, it works fine. 
> 
> I use 32-bit buildroot (and debian) rootfs images all the time on
> Amlogic SoCs with 64-bit kernels and it works fine.  

You are totally right. It's one of the possible ways. But in the our
internal project we build kernel + roofs + uboot together in the one
buildroot project ('repo' based). So we will try to stay in the such
paradigm, but will use multi-arch toolchain, maybe.
Anyway, thanks a lot for sharing your experience.

-- 
Thank you,
Dmitry