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Date:   Sun, 28 Mar 2021 23:58:07 +0200
From:   Willy Tarreau <w@1wt.eu>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Mateusz Jonczyk <mat.jonczyk@o2.pl>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Testers wanted: Atom netbooks with x86_64 disabled by BIOS
Message-ID: <20210328215807.GA26428@1wt.eu>
References: <20210327203218.119372-1-mat.jonczyk@o2.pl>
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 <20210327232551.GA20783@1wt.eu>
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 <20210328061837.GA22710@1wt.eu>
 <CAHp75Ve_Yhs3ib5yk=d-+bhb4vHpx-j6D4jGGBKuD2k1qv38Vg@mail.gmail.com>
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On Sun, Mar 28, 2021 at 11:14:05PM +0300, Andy Shevchenko wrote:
> On Sunday, March 28, 2021, Willy Tarreau <w@1wt.eu> wrote:
> 
> > Hi Thomas,
> >
> > On Sun, Mar 28, 2021 at 03:07:24AM +0200, Thomas Gleixner wrote:
> > > On Sun, Mar 28 2021 at 00:25, Willy Tarreau wrote:
> > > > On Sat, Mar 27, 2021 at 10:13:22PM +0100, Mateusz Jonczyk wrote:
> > > > FWIW I tested on my ASUS 1025C which runs on an Atom N2600 forced to
> > > > 32-bit. I had already tried in the past but wanted to give it a try
> > > > again in case I'd have missed anything. Sadly it didn't work, I'm
> > > > still getting the "requires an x86-64 CPU" message.
> > > >
> > > > Given these machines were really cheap, I've always suspected that they
> > > > employ cheaper, low-grade CPUs, possibly having been subject to reduced
> > > > tests where x86_64-specific parts were not even verified and might be
> > > > defective. This may explain why they forcefully disable long mode
> > there,
> > > > but that's just speculation.
> > >
> > > There are some of these '32bit only' CPUs out there in the wild which
> > > actually support long mode. Some of them even do not have the long mode
> > > CPUID bit fused out.
> >
> > Yes, I'm aware of this as well. We might even have talked to the same
> > "victim" :-)
> >
> > > But whether it works is a different story:
> > >
> > >   - If the CPUID bit is on, then the chance is high, but it runs out of
> > >     spec (guarantee wise)
> > >
> > >   - If it's off is still might work by some definition of work as they
> > >     might have fused off more or there are actual defects in some 64bit
> > >     only area which are irrelevant when in 32bit mode.
> > >
> > > Even if it could work perfectly fine, the BIOS/SMM/ucode can prevent
> > > switching to long mode.
> > >
> > > It's a lost cause.
> >
> > I agree. While I bought this netbook to have a 64-bit CPU and was extremely
> > disappointed,
> 
> 
> Where did you get an idea that it had 64-bit SoC from?

It's an N2600, and I bought this laptop because N2600 supports 64-bit
(and do have another mini-itx motherboard at work with the same CPU
on it working pretty well in 64-bit):

   https://ark.intel.com/content/www/us/en/ark/products/58916/intel-atom-processor-n2600-1m-cache-1-6-ghz.html

> Atom Based 64-bit ones are Bay Trail, Cherry Trail, Tangier (Merrifield),
> Anniedale (Moorefield) and all based on Skylake family (Apollo Lake,
> Broxton, Gemini Lake, ...).

Well, to be honest, I've never been able to remind (nor sort) all these
totally crazy names. The day someone gives me a mnemotechnic hint to
remind them and their ordering, that will make me reconsider them. For
now they're all "something lake", and I find it particularly difficult
to map them to SKUs.

Cheers,
Willy