linux-kernel - Re: [PATCH] arm64: dts: qcom: x1e: bus is 40-bits (fix 64GB models)

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Message-ID: <CAOvMTZhartq70YBCkGHbNNYd4MK1RqCjwoV3-WhrHoEqEtgLTA@mail.gmail.com>
Date: Sun, 30 Nov 2025 20:25:17 -0600
From: Steev Klimaszewski <threeway@...il.com>
To: Jonathan Marek <jonathan@...ek.ca>
Cc: abel.vesa@...aro.org, andersson@...nel.org, christopher.obbard@...aro.org, 
	conor+dt@...nel.org, devicetree@...r.kernel.org, konradybcio@...nel.org, 
	krzk+dt@...nel.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, quic_rjendra@...cinc.com, robh@...nel.org, 
	sibi.sankar@....qualcomm.com, stephan.gerhold@...aro.org
Subject: Re: [PATCH] arm64: dts: qcom: x1e: bus is 40-bits (fix 64GB models)

Hi Jonathan,

On Sun, Nov 30, 2025 at 8:07 PM Jonathan Marek <jonathan@...ek.ca> wrote:
>
> I was curious about this so I tried booting EL1
> - 32GB CRD boots fine
> - 64GB T14S boots with CONFIG_ARM64_VA_BITS_39 (except display driver
> didn't probe, because it depends on adsp firmware, lol). without
> CONFIG_ARM64_VA_BITS_39 it resets

Weird, I definitely have CONFIG_ARM64_VA_BITS_39 set here.

>
> Anyway making things worse for "64GB+EL1+broken firmware" shouldn't
> block this patch, because "64GB+EL1+broken firmware" needs workarounds
> anyway and this change is needed to use 64GB without issues otherwise.

I'm not sure I follow this logic; most users when they first get the
system will be stuck in el1 until they get el2 set up, which also
requires workarounds in order to set up.  I don't at all disagree that
the fix is more correct, but I don't like users having broken things
just because the vendor hasn't fixed their firmware yet.
Additionally, distro kernels will default to BITS_52 for arm64
kernels, not 39 because most of them run more places than just
Qualcomm laptops.

>
> On 11/30/25 7:13 PM, Steev Klimaszewski wrote:
> > Hi All,
> >
> > On my Thinkpad T14S OLED with 64GB, with this patch applied, I am unable to boot
> > the laptop anymore.  It doesn't matter whether I have mem=30GB, nor if I set
> > CONFIG_ARM64_VA_BITS_39, or not limiting the ram - shortly after loading the
> > device tree, the laptop just resets.
> >
> > I have tried over 20 boots with it applied, as well as trying both booting a
> > working kernel, and then rebooting as well as cold boots.
> >
> >
> > -- steev
> >
> .