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

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Message-ID: <35615ad4-5b86-577f-4695-c6cd85206334@marek.ca>
Date: Fri, 28 Nov 2025 18:56:55 -0500
From: Jonathan Marek <jonathan@...ek.ca>
To: Christopher Obbard <christopher.obbard@...aro.org>
Cc: Stephan Gerhold <stephan.gerhold@...aro.org>,
 linux-arm-msm@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Sibi Sankar <sibi.sankar@....qualcomm.com>,
 Abel Vesa <abel.vesa@...aro.org>, Rajendra Nayak <quic_rjendra@...cinc.com>,
 "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: qcom: x1e: bus is 40-bits (fix 64GB models)

FYI, for a less hacky solution you can use CONFIG_ARM64_VA_BITS_39, 
arm64 linux as-is refuses to use any memory it can't identity map (and 
the extra 32GB of memory is outside the 39-bit range).

On 11/28/25 5:10 PM, Christopher Obbard wrote:
> Hi,
> 
> Sorry to hijack this thread, but I've been carrying this patch to
> workaround the buggy firmware from Stephan for my Lenovo T14s with
> 64gb RAM which seems to make Linux boot & work just fine with
> systemd-boot.
> Of course, it's a hack and not ready for upstream.
> 
> On another topic, perhaps we need to add this to
> https://gitlab.com/Linaro/arm64-laptops/linux , what do you think
> Stephan ?
> 
> Chris
> 
> 
> commit 16e21600c6a65ace0c75b5a722e27ced8e1bfc48
> Author: Stephan Gerhold <stephan.gerhold@...aro.org>
> Date:   Thu Mar 6 17:41:15 2025 +0000
> 
>      HACK: efi-stub: Exclude 40-bit memory
> 
> diff --git a/drivers/firmware/efi/libstub/efi-stub.c
> b/drivers/firmware/efi/libstub/efi-stub.c
> index 874f63b4a383..355a9b2c0818 100644
> --- a/drivers/firmware/efi/libstub/efi-stub.c
> +++ b/drivers/firmware/efi/libstub/efi-stub.c
> @@ -106,6 +106,17 @@ efi_status_t
> efi_handle_cmdline(efi_loaded_image_t *image, char **cmdline_ptr)
>   {
>          char *cmdline __free(efi_pool) = NULL;
>          efi_status_t status;
> +       efi_physical_addr_t addr;
> +       unsigned long pages;
> +
> +       addr = 0x0000008800000000;
> +       pages = 0x800000000 / EFI_PAGE_SIZE;
> +       status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
> +                                                EFI_RESERVED_TYPE,
> pages, &addr);
> +       if (status != EFI_SUCCESS) {
> +               efi_err("failed to reserve upper 32 GiB (40-bit memory)\n");
> +               return EFI_OUT_OF_RESOURCES;
> +       }
> 
>          /*
>           * Get the command line from EFI, using the LOADED_IMAGE
> 
> 
> 
> 
> Cheers!
> 
> Chris
> 
>