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Re: [PATCH v3 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT

by Ilias Apalodimas

Hi Adriana, On Fri, 31 Oct 2025 at 10:41, adriana <adriana(a)arista.com> wrote: > > From: Adriana Nicolae <adriana(a)arista.com> We'll need a description of why the change is needed here. [...] > > #ifndef SMBIOS_ENTRY_POINT_SCAN_START > #define SMBIOS_ENTRY_POINT_SCAN_START 0xF0000 > @@ -670,6 +673,54 @@ static int __init dmi_smbios3_present(const u8 *buf) > return 1; > } > > +#if IS_ENABLED(CONFIG_OF) > +/** > + * dmi_scan_from_dt - Find and parse DMI/SMBIOS tables from the Device Tree > + * > + * Checks if the bootloader has passed SMBIOS table addresses via the /chosen > + * node in the Device Tree. This follows the standard kernel DT bindings and > + * assumes a fixed 32-byte mapping for the entry point. > + * Returns true if a valid table is found and successfully parsed. > + */ > +static bool __init dmi_scan_from_dt(void) > +{ > + struct device_node *chosen; > + const __be64 *prop; > + char buf[32]; > + void __iomem *p; > + bool dmi_available = false; > + u64 addr; > + int len; > + > + chosen = of_find_node_by_path("/chosen"); > + if (!chosen) > + return false; > + > + prop = of_get_property(chosen, "linux,smbios3-table", &len); > + if (prop && len >= sizeof(u64)) { > + addr = be64_to_cpup(prop); > + > + p = dmi_early_remap(addr, 32); Please put '32' into a define that explains what it is > + if (p == NULL) I think if (!p) is preferred > + goto out; > + > + memcpy_fromio(buf, p, sizeof(buf)); > + dmi_early_unmap(p, 32); > + > + if (!dmi_smbios3_present(buf)) { > + dmi_available = true; > + goto out; > + } > + } > + > +out: > + of_node_put(chosen); > + return dmi_available; > +} > +#else > +static bool __init dmi_scan_from_dt(void) { return false; } > +#endif /* IS_ENABLED(CONFIG_OF) */ > + > static void __init dmi_scan_machine(void) > { > char __iomem *p, *q; > @@ -718,6 +769,13 @@ static void __init dmi_scan_machine(void) > dmi_available = 1; > return; > } > + } else if (IS_ENABLED(CONFIG_OF) && dmi_scan_from_dt()) { Can you fold the IS_ENABLED() in dmi_scan_from_dt() please? > + /* [...] Thanks /Ilias

11 months, 3 weeks

Re: [PATCH v3 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT

by Ard Biesheuvel

Hello Adriana, On Fri, 31 Oct 2025 at 09:41, adriana <adriana(a)arista.com> wrote: > > From: Adriana Nicolae <adriana(a)arista.com> > > Signed-off-by: Adriana Nicolae <adriana(a)arista.com> > --- > drivers/firmware/dmi_scan.c | 58 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 58 insertions(+) > > diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c > index 70d39adf50dc..acc0e18b8d0f 100644 > --- a/drivers/firmware/dmi_scan.c > +++ b/drivers/firmware/dmi_scan.c > @@ -10,6 +10,9 @@ > #include <linux/random.h> > #include <asm/dmi.h> > #include <linux/unaligned.h> > +#if IS_ENABLED(CONFIG_OF) > +#include <linux/of.h> > +#endif > > #ifndef SMBIOS_ENTRY_POINT_SCAN_START > #define SMBIOS_ENTRY_POINT_SCAN_START 0xF0000 > @@ -670,6 +673,54 @@ static int __init dmi_smbios3_present(const u8 *buf) > return 1; > } > > +#if IS_ENABLED(CONFIG_OF) > +/** > + * dmi_scan_from_dt - Find and parse DMI/SMBIOS tables from the Device Tree > + * > + * Checks if the bootloader has passed SMBIOS table addresses via the /chosen > + * node in the Device Tree. This follows the standard kernel DT bindings and > + * assumes a fixed 32-byte mapping for the entry point. Not sure what 'the standard kernel DT bindings' are, or what you mean by 'a fixed 32-byte mapping. You could just drop this sentence, I think, or otherwise, describe that the DT property gives us the physical address of the SMBIOS3 entrypoint structure. > + * Returns true if a valid table is found and successfully parsed. if a valid entry point is found > + */ > +static bool __init dmi_scan_from_dt(void) > +{ > + struct device_node *chosen; > + const __be64 *prop; > + char buf[32]; > + void __iomem *p; > + bool dmi_available = false; > + u64 addr; > + int len; > + > + chosen = of_find_node_by_path("/chosen"); > + if (!chosen) > + return false; > + > + prop = of_get_property(chosen, "linux,smbios3-table", &len); > + if (prop && len >= sizeof(u64)) { > + addr = be64_to_cpup(prop); > + > + p = dmi_early_remap(addr, 32); > + if (p == NULL) > + goto out; > + > + memcpy_fromio(buf, p, sizeof(buf)); > + dmi_early_unmap(p, 32); > + > + if (!dmi_smbios3_present(buf)) { > + dmi_available = true; > + goto out; > + } > + } > + > +out: > + of_node_put(chosen); > + return dmi_available; > +} > +#else > +static bool __init dmi_scan_from_dt(void) { return false; } > +#endif /* IS_ENABLED(CONFIG_OF) */ > + > static void __init dmi_scan_machine(void) > { > char __iomem *p, *q; > @@ -718,6 +769,13 @@ static void __init dmi_scan_machine(void) > dmi_available = 1; > return; > } > + } else if (IS_ENABLED(CONFIG_OF) && dmi_scan_from_dt()) { Please drop the IS_ENABLED() here, and fold it into dmi_scan_from_dt(), by doing if (!IS_ENABLED(CONFIG_OF)) return false; at the beginning. This removes the need to provide two different versions of dmi_scan_from_dt(). > + /* > + * If EFI is not present or failed, try getting SMBIOS > + * tables from the Device Tree. > + */ > + dmi_available = 1; > + return; > } else if (IS_ENABLED(CONFIG_DMI_SCAN_MACHINE_NON_EFI_FALLBACK)) { > p = dmi_early_remap(SMBIOS_ENTRY_POINT_SCAN_START, 0x10000); > if (p == NULL) > -- > 2.51.0 >

11 months, 3 weeks

Re: [PATCH v3 1/2] dt-bindings: firmware: Add binding for SMBIOS /chosen properties

by Ard Biesheuvel

On Fri, 31 Oct 2025 at 09:41, adriana <adriana(a)arista.com> wrote: > > From: Adriana Nicolae <adriana(a)arista.com> > > Signed-off-by: Adriana Nicolae <adriana(a)arista.com> > --- > .../bindings/firmware/linux,smbios-table.yaml | 26 +++++++++++++++++++ > 1 file changed, 26 insertions(+) > create mode 100644 Documentation/devicetree/bindings/firmware/linux,smbios-table.yaml > > diff --git a/Documentation/devicetree/bindings/firmware/linux,smbios-table.yaml b/Documentation/devicetree/bindings/firmware/linux,smbios-table.yaml > new file mode 100644 > index 000000000000..b78d8ec6025f > --- /dev/null > +++ b/Documentation/devicetree/bindings/firmware/linux,smbios-table.yaml > @@ -0,0 +1,26 @@ > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) > +# Copyright 2025 Arista Networks > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/firmware/linux,smbios-table.yaml# Should the file name reflect the property? I.e., linux,smbios3-table.yaml > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: Memory location for SMBIOS table > + > +description: | > + This property is used in the /chosen node to pass the physical address > + of SMBIOS (System Management BIOS) or DMI (Desktop Management Interface) > + tables from firmware to the kernel. This is typically used on non-EFI > + platforms like ARM/ARM64. > + 'like ARM/ARM64' is both unnecessary and inaccurate, so better to drop it. > +maintainers: > + - Adriana Nicolae <adriana(a)arista.com> > + - Rob Herring <robh+dt(a)kernel.org> > + > +properties: > + linux,smbios3-table: > + $ref: /schemas/types.yaml#/definitions/uint64 > + description: > + The 64-bit physical address of the SMBIOSv3 entry point structure. > + > +additionalProperties: true > -- > 2.51.0 >

11 months, 3 weeks

Re: [PATCH v2 0/2] DMI: Scan for DMI table from DTS info

by Ard Biesheuvel

On Thu, 23 Oct 2025 at 16:48, Adriana Nicolae <adriana(a)arista.com> wrote: > > On Thu, Oct 23, 2025 at 4:54 PM Ard Biesheuvel <ardb(a)kernel.org> wrote: > > > > (cc Ilias) > > > > On Thu, 23 Oct 2025 at 15:34, Adriana Nicolae <adriana(a)arista.com> wrote: > > > > > > On Thu, Oct 23, 2025 at 11:21 AM Ard Biesheuvel <ardb(a)kernel.org> wrote: > > > > > > > > On Thu, 23 Oct 2025 at 04:21, Adriana Nicolae <adriana(a)arista.com> wrote: > > > > > > > > > > On Wed, Oct 22, 2025 at 11:19 PM Rob Herring <robh(a)kernel.org> wrote: > > > > > > > > > > > > On Wed, Oct 22, 2025 at 04:45:25AM -0700, adriana wrote: > > > > > > > Some bootloaders like U-boot, particularly for the ARM architecture, > > > > > > > provide SMBIOS/DMI tables at a specific memory address. However, these > > > > > > > systems often do not boot using a full UEFI environment, which means the > > > > > > > kernel's standard EFI DMI scanner cannot find these tables. > > > > > > > > > > > > I thought u-boot is a pretty complete UEFI implementation now. If > > > > > > there's standard way for UEFI to provide this, then that's what we > > > > > > should be using. I know supporting this has been discussed in context of > > > > > > EBBR spec, but no one involved in that has been CC'ed here. > > > > > > > > > > Regarding the use of UEFI, the non UEFI boot is used on Broadcom iProc which > > > > > boots initially into a Hardware Security Module which validates U-boot and then > > > > > loads it. This specific path does not utilize U-Boot's UEFI > > > > > implementation or the > > > > > standard UEFI boot services to pass tables like SMBIOS. > > > > > > > > > > > > > What prevents this HSM validated copy of u-boot from loading the kernel via EFI? > > > The vendor's U-Boot configuration for this specific secure boot path > > > (involving the > > > HSM) explicitly disables the CMD_BOOTEFI option due to security > > > mitigations, only > > > a subset of U-boot commands are whitelisted. We could patch the U-boot > > > to include > > > that but it is preferable to follow the vendor's recommandations and > > > just patch U-boot > > > to fill that memory location with SMBIOS address or directly with the > > > entry point. > > > > And what security mitigations are deemed needed for the EFI code? You > > are aware that avoiding EFI boot means that the booting kernel keeps > > all memory protections disabled for longer than it would otherwise. Is > > this allowlisting based on simply minimizing the code footprint? > > > From the information I have, it might be just minimizing the footprint > but the vendor's U-Boot configuration for this specific path > explicitly disables the CMD_BOOTEFI option. While the vendor cites > security mitigations for this configuration, the specific details > could be a set of mitigation removing different boot methods and some > memory access commands. > > The core issue is that this non-EFI boot path is the vendor-validated > configuration. Enabling EFI would deviate from this setup, require > significant revalidation, and could impact vendor support. Modifying > U-Boot to populate the DT is a contained change without modifying the > U-boot vendor configuration. > I'm not sure I follow why changing U-Boot's code would not require revalidation if simply changing its build configuration without modifying the source code would require that. > Beyond our specific vendor constraints, this DT method might be used > by any other non-UEFI arm system needing to expose SMBIOS tables to > the kernel. > Fair point. So let's do this properly: get buy-in from the U-Boot folks and contribute your u-boot changes as well. And ideally, we'd get this into the DMTF spec but if you are not set up for that (I think you might need to be a member to be able to contribute), we can find some ARM folks who are.

12 months

Re: [PATCH v2 0/2] DMI: Scan for DMI table from DTS info

by Ard Biesheuvel

(cc Ilias) On Thu, 23 Oct 2025 at 15:34, Adriana Nicolae <adriana(a)arista.com> wrote: > > On Thu, Oct 23, 2025 at 11:21 AM Ard Biesheuvel <ardb(a)kernel.org> wrote: > > > > On Thu, 23 Oct 2025 at 04:21, Adriana Nicolae <adriana(a)arista.com> wrote: > > > > > > On Wed, Oct 22, 2025 at 11:19 PM Rob Herring <robh(a)kernel.org> wrote: > > > > > > > > On Wed, Oct 22, 2025 at 04:45:25AM -0700, adriana wrote: > > > > > Some bootloaders like U-boot, particularly for the ARM architecture, > > > > > provide SMBIOS/DMI tables at a specific memory address. However, these > > > > > systems often do not boot using a full UEFI environment, which means the > > > > > kernel's standard EFI DMI scanner cannot find these tables. > > > > > > > > I thought u-boot is a pretty complete UEFI implementation now. If > > > > there's standard way for UEFI to provide this, then that's what we > > > > should be using. I know supporting this has been discussed in context of > > > > EBBR spec, but no one involved in that has been CC'ed here. > > > > > > Regarding the use of UEFI, the non UEFI boot is used on Broadcom iProc which > > > boots initially into a Hardware Security Module which validates U-boot and then > > > loads it. This specific path does not utilize U-Boot's UEFI > > > implementation or the > > > standard UEFI boot services to pass tables like SMBIOS. > > > > > > > What prevents this HSM validated copy of u-boot from loading the kernel via EFI? > The vendor's U-Boot configuration for this specific secure boot path > (involving the > HSM) explicitly disables the CMD_BOOTEFI option due to security > mitigations, only > a subset of U-boot commands are whitelisted. We could patch the U-boot > to include > that but it is preferable to follow the vendor's recommandations and > just patch U-boot > to fill that memory location with SMBIOS address or directly with the > entry point. And what security mitigations are deemed needed for the EFI code? You are aware that avoiding EFI boot means that the booting kernel keeps all memory protections disabled for longer than it would otherwise. Is this allowlisting based on simply minimizing the code footprint? Introducing a non-standard mechanism means that others will now have to maintain it and coexist with it, rather than simply using the existing code which already fully supports what you are trying to accomplish (both on the bootloader and the kernel side) IOW, in my opinion, simply enabling CMD_BOOTEFI for your bootloader is a much better choice here. I'm not a u-boot expert but as I understand it, loading/authenticating the image and booting it in EFI mode are two separate things, and so the secure boot path would change very little. > > > Because there's no UEFI configuration table available in this boot mode, we need > > > an alternative mechanism to pass the SMBIOS table address to the kernel. The > > > /chosen node seemed like the most straightforward way for the bootloader to > > > communicate this non-discoverable information. > > > > > > I wasn't aware of the EBBR discussions covering this. I've added the > > > boot-architecture and arm.ebbr-discuss lists to the Cc. If there's a preferred > > > EBBR-compliant way to handle this for non-UEFI boots, I'm happy to adapt > > > the approach. > > > > > > > For the record, I don't see a huge problem with accepting SMBIOS > > tables in this manner, but it would be better if a description of this > > method was contributed to the DMTF spec, which currently states that > > the only way to discover SMBIOS tables on non-x86 systems is via the > > SMBIOS/SMBIOS3 EFI configuration tables. Doing so should prevent other > > folks from inventing their own methods for their own vertically > > integrated systems. (Other OSes exist, and from a boot arch PoV, we > > try to avoid these Linux-only shortcuts) > > > > However, the DT method should *only* be used when not booting via > > UEFI, to avoid future surprises, and to ensure that existing OSes > > (including older Linux) can always find the SMBIOS tables when booting > > via UEFI. > > > > Also, I would suggest to pull the entire entrypoint into DT, rather > > than the address in memory of either/both entrypoint(s). Both just > > carry some version fields, and the address of the actual SMBIOS data > > in memory, and the only difference between SMBIOS and SMBIOS3 is the > > size of the address field (32 vs 64 bits) > I understand the points raised about UEFI taking precedence and the > preference for standardization (DMTF). If this DT method is accepted > as a fallback only for non-UEFI boots like this one, the kernel implementation > will respect that precedence. > > Regarding the alternative to place the full SMBIOS entry point structure into > a DT property (as a byte array) instead of just its memory address. Both > approaches seem feasible from the U-Boot side. I opted initially for passing > the address to reuse the existing kernel functions (dmi_smbios3_present and > dmi_present) which already handle mapping and validation of the entry point > read from memory (as done for the EFI case). > Actually, it appears that dmidecode expects the entrypoint data in /sys/firmware/dmi/tables/smbios_entry_point, and so you will need to populate that file in any case, and so pulling it into the DT node is not as useful. But having both SMBIOS and SMBIOS3 is pointless, so please only bother with the latter.

12 months

Re: [PATCH v2 0/2] DMI: Scan for DMI table from DTS info

by Ard Biesheuvel

On Thu, 23 Oct 2025 at 04:21, Adriana Nicolae <adriana(a)arista.com> wrote: > > On Wed, Oct 22, 2025 at 11:19 PM Rob Herring <robh(a)kernel.org> wrote: > > > > On Wed, Oct 22, 2025 at 04:45:25AM -0700, adriana wrote: > > > Some bootloaders like U-boot, particularly for the ARM architecture, > > > provide SMBIOS/DMI tables at a specific memory address. However, these > > > systems often do not boot using a full UEFI environment, which means the > > > kernel's standard EFI DMI scanner cannot find these tables. > > > > I thought u-boot is a pretty complete UEFI implementation now. If > > there's standard way for UEFI to provide this, then that's what we > > should be using. I know supporting this has been discussed in context of > > EBBR spec, but no one involved in that has been CC'ed here. > > Regarding the use of UEFI, the non UEFI boot is used on Broadcom iProc which > boots initially into a Hardware Security Module which validates U-boot and then > loads it. This specific path does not utilize U-Boot's UEFI > implementation or the > standard UEFI boot services to pass tables like SMBIOS. > What prevents this HSM validated copy of u-boot from loading the kernel via EFI? > Because there's no UEFI configuration table available in this boot mode, we need > an alternative mechanism to pass the SMBIOS table address to the kernel. The > /chosen node seemed like the most straightforward way for the bootloader to > communicate this non-discoverable information. > > I wasn't aware of the EBBR discussions covering this. I've added the > boot-architecture and arm.ebbr-discuss lists to the Cc. If there's a preferred > EBBR-compliant way to handle this for non-UEFI boots, I'm happy to adapt > the approach. > For the record, I don't see a huge problem with accepting SMBIOS tables in this manner, but it would be better if a description of this method was contributed to the DMTF spec, which currently states that the only way to discover SMBIOS tables on non-x86 systems is via the SMBIOS/SMBIOS3 EFI configuration tables. Doing so should prevent other folks from inventing their own methods for their own vertically integrated systems. (Other OSes exist, and from a boot arch PoV, we try to avoid these Linux-only shortcuts) However, the DT method should *only* be used when not booting via UEFI, to avoid future surprises, and to ensure that existing OSes (including older Linux) can always find the SMBIOS tables when booting via UEFI. Also, I would suggest to pull the entire entrypoint into DT, rather than the address in memory of either/both entrypoint(s). Both just carry some version fields, and the address of the actual SMBIOS data in memory, and the only difference between SMBIOS and SMBIOS3 is the size of the address field (32 vs 64 bits)

1 year

EBBR call today Oct 22

by Vincent Stehlé

Dear EBBR contributors, We will have our EBBR call today, Oct 22 at 14:00 BST (13:00 UTC). [1] We have two pull requests on the agenda [2]: - Pull request #142: SCMI requirements - Pull request #148: Fix bibliography alignment for PDF and HTML We will use this pad [3] for the meeting notes. Feel free to add to the agenda, directly on the wiki page, by e-mail or on the pad. Best regards, Vincent Stehlé System Architect - Arm [1] https://armltd.zoom.us/j/92081365511?pwd=SFZpRitXUEp3Zy9GM0h3UUZ1b1pnUT09 [2] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings [3] https://mensuel.framapad.org/p/ebbr-call-of-oct-22-ahgu?lang=en #142: https://github.com/ARM-software/ebbr/pull/142 #148: https://github.com/ARM-software/ebbr/pull/148

1 year

EBBR call today Oct 8

by Vincent Stehlé

Dear EBBR contributors, We will have our EBBR call today, Oct 8 at 14:00 BST (13:00 UTC). [1] We have mostly one pull request on the agenda [2]: - Pull request #142: SCMI requirements This is less important but if time permits, we can also discuss this second pull request: - Pull request #148: Fix bibliography alignment for PDF and HTML We will use this pad [3] for the meeting notes. Feel free to add to the agenda, directly on the wiki page, by e-mail or on the pad. Best regards, Vincent Stehlé System Architect - Arm [1] https://armltd.zoom.us/j/92081365511?pwd=SFZpRitXUEp3Zy9GM0h3UUZ1b1pnUT09 [2] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings [3] https://mensuel.framapad.org/p/ebbr-call-of-oct-8-ah7i?lang=en #142: https://github.com/ARM-software/ebbr/pull/142 #148: https://github.com/ARM-software/ebbr/pull/148

1 year

DT relevance

by ff

Dear fellow firmware aficionados, Static ACPI has been adopted by Mercedes and other silicon vendors to: - meet the safety requirements - stay away from DT lifecycle issues - leverage chiplet and CXL bindings - truly multi-host/hypervisor (or even secure/no-secure should people want it) as bindings are defined in an ad-hoc forum (not by an OS community) DT community leaders and enthusiasts, I believe discussion on the bigger picture related to DT relevance in the long run may be needed as I believe many embedded solutions will follow Mercedes example. Constructively yours, François-Frédéric PS: static ACPI can be handled by a simple parser, do not execute any ACPI byte code, is findable by EFI tables, code base is even smaller than libfdt.

1 year

EBBR call today Sep 24

by Vincent Stehlé

Dear EBBR contributors, We will have our EBBR call today, Sep 24 at 14:00 BST (13:00 UTC). [1] We have a single topic on the agenda [2]: - Pull request #142: SCMI requirements (was: "Conditionally require SCMI 2.x, x >= 1 recommended") Feel free to add to the agenda, directly on the wiki page, by e-mail or on the pad. We will use this pad [3] for the meeting notes. Best regards, Vincent Stehlé System Architect - Arm [1] https://armltd.zoom.us/j/92081365511?pwd=SFZpRitXUEp3Zy9GM0h3UUZ1b1pnUT09 [2] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings [3] https://mensuel.framapad.org/p/ebbr-call-of-sep-24-agy7?lang=en #142: https://github.com/ARM-software/ebbr/pull/142

1 year

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