boot-architecture

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6 participants
667 discussions

by Vincent Stehle

(This is a resend; sorry if you receive this e-mail twice.) Dear EBBR contributors, We will have our EBBR call today, Nov 19 at 14:00 UTC. [1] We have four pull requests on the agenda [2]: - Pull request #151: references: update RISC-V references - Pull request #152: Recommend firmware TRNG - Pull request #153: Add a note on SMCCC conduits - Pull request #154: Recommend the SOC_ID SMCCC call We will use this pad [3] for the meeting notes. Feel free to add topics 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-nov-19-ahzj?lang=en #151: https://github.com/ARM-software/ebbr/pull/151 #152: https://github.com/ARM-software/ebbr/pull/152 #153: https://github.com/ARM-software/ebbr/pull/153 #154: https://github.com/ARM-software/ebbr/pull/154 IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

1 week, 1 day

EBBR call today Nov 19

by Vincent Stehlé

Dear EBBR contributors, We will have our EBBR call today, Nov 19 at 14:00 UTC. [1] We have four pull requests on the agenda [2]: - Pull request #151: references: update RISC-V references - Pull request #152: Recommend firmware TRNG - Pull request #153: Add a note on SMCCC conduits - Pull request #154: Recommend the SOC_ID SMCCC call We will use this pad [3] for the meeting notes. Feel free to add topics 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-nov-19-ahzj?lang=en #151: https://github.com/ARM-software/ebbr/pull/151 #152: https://github.com/ARM-software/ebbr/pull/152 #153: https://github.com/ARM-software/ebbr/pull/153 #154: https://github.com/ARM-software/ebbr/pull/154

1 week, 1 day

Proposal: Officially allow "incomplete" trees as a base

by Doug Anderson

This is a continuation of the discussion that started in reply to my patch adding basic device trees for Pixel 10 phones [1]. Problem statement: ------------------ We would like an officially accepted scheme that lets us more efficiently ship compiled device trees for a handful of related products by breaking the device trees up into a common "base" device tree and then applying "overlay" device trees atop the base to make a full and complete device tree. To make it more concrete, we'd like to build a "base" device tree that describes a SoC and then have the overlays be enough to make a full description of a board. In theory, one could also imagine wanting to expand this to 3 or more levels (perhaps SoC, baseboard, derived boards), though this is not planned at this time. The primary reason for wanting to break device trees like this is efficiency of the shipped binary device trees. A large portion of a final device tree just describes the SoC. We save space in the final compiled device trees if they don't need to contain as much duplicated information. A secondary reason for wanting to break device trees like this is to more nicely handle when a board has a socketed SoC that can be replaced with a finite (and small) number of different SoCs (usually revisions of the same SoC). Even if this secondary reason is considered invalid or too difficult, the primary reason still describes a compelling need. In order to make this proposal work, it's expected that a bootloader will understand the scheme and will know how to combine the overlay atop the base before passing a complete device tree to the main OS. Current state of the art (downstream): -------------------------------------- In Android, we do a pretty good job of solving the stated problem using device tree overlays. We describe the SoCs in "dts" files and compile them into "dtb"s. We describe boards in "dtso" files and compile them into "dtbo" files. A bootloader can handle identifying the correct base and overlay (the scheme for doing this is a separate but related topic) and applying the overlay atop the base "dtb". This solution is fully implemented downstream for Android phones and is well documented [2]. The issues I'm aware of with the current state of the art are: 1. In order for the base device tree to pass schema validation on its own we'd need to document the top-level compatible strings in the device tree. It is the opinion of at least some device tree maintainers that a SoC doesn't qualify as a top-level compatible string. This prevents the device trees from landing in an officially sanctioned location. 2. It is also possible we may fail schema validation for the base SoC tree if the schema marks a property as "required" but that property needs to be filled out by the board (perhaps a "-supply" is marked as "required", since most "-supply" properties are filled in by the board. I'm not sure this is a big issue, but it's something to think about. 3. It's unclear if there is any official "ABI" promised here once we've compiled and validated the base device tree on its own. Will people assume that they can have out-of-tree overlays derived from the base SoC tree and that those out-of-tree overlays will continue to work across changes / cleanups to the base? NOTE: this is a pre-existing question for existing device tree overlay usage, but the sheer quantity of nodes/properties that a board would be expected to overlay/modify in the base make the problem more prominent. 4. We want the final device tree's top-level compatible to be all the compatible strings from the board followed by all of the compatible strings for the SoC. When the board's overlay is applied to the base SoC tree, though, the board's top-level compatible fully replaces the compatible from the base SoC tree. This can be solved today for non-socketed boards by just duplicating the SoC compatible strings in the board overlays. We can't solve this today for socketed boards, though we can simply make sure that no software drivers rely on the specific SoC compatible string being present and thus we can ignore the problem. None of the above problems are big enough to have prevented widespread use of this scheme in downstream Android. Current state of the art (upstream): ------------------------------------ Upstream if we have a pile of related boards, we do allow deduplicating things at a source-code level with "dtsi" files. We can have a SoC "dtsi" file and that file is included by all boards that use that SoC. When it comes time to validate or ship things, though, we only work with full devices trees. This means that we ship duplicated information. Proposal: --------- 1. Allow the top-level compatible string of an "incomplete" device tree to be documented so it can be validated on its own by tools. It's understood that this SoC is not a board by itself and we'd never boot a full OS with this device tree without adding an overlay that changes the top-level compatible. Add a top-level property to the device tree (perhaps "incomplete-compatible;") to indicate that the tree is not complete without an overlay. 2. If it turns out to be needed (hopefully it's not), allow some type of syntax in yaml files that allows a property to be marked as "required" in a "complete" device tree but not in an "incomplete" device tree. Alternatively, we could discourage marking properties as "required" if they're expected to be filled in by a board. 3. Define that there is no promised ABI between "incomplete" device trees and anything not stored with them. Specifically, all valid combinations of "incomplete" device trees with overlays to complete them should be enumerated together with the "incomplete" device tree. 4. When applying an overlay to a device tree that's "incomplete", the top level overlay will be merged instead of replaced. Example for 2 levels: base (incomplete) compatible: "socvendor,mysoc-rev1", "socvendor,mysoc"; overlay compatible: "boardvendor,myboard-rev1", "boardvendor,myboard"; merged compatible: "boardvendor,myboard-rev1", "boardvendor,myboard", "socvendor,mysoc-rev1", "socvendor,mysoc"; Possible example if we support 3 levels: SoC (incomplete) compatible: "socvendor,mysoc-rev1", "socvendor,mysoc" overlay1 (incomplete) compatible: "referencevendor,referencecodename"; overlay2 compatible: "boardvendor,myboard-rev1", "boardvendor,myboard" merged compatible: "boardvendor,myboard-rev1", "boardvendor,myboard", "referencevendor,reference-codename", "socvendor,mysoc-rev1", "socvendor,mysoc"; Obviously in the 3-level scheme we need to know the order that overlays are applied, but that's true for overlays today anyway. The above proposal takes the current downstream "state of the art" and addresses the known issues, solving the original problem statement. Other thoughts: --------------- If you don't like the proposal, I'd be interested in knowing if you have other ideas for solving the original problem statement, or if you simply think the problem we're trying to solve here is an invalid one. I'm happy to post up another revision of my Pixel 10 device trees following this proof of concept (or other ones). My v1 was _very_ close to this, but didn't have the "incomplete-compatible;" property and didn't implement top-level compatible merging. [1] https://lore.kernel.org/r/20251111112158.1.I72a0b72562b85d02fee424fed939fea… [2] https://source.android.com/docs/core/architecture/dto/partitions

1 week, 2 days

EBBR call today Nov 5

by Vincent Stehlé

Dear EBBR contributors, We will have our EBBR call today, Nov 5 at 14:00 UTC. [1] Note: BST is not observed anymore. The call will begin at 14:00 UTC. We have four pull requests on the agenda [2]: - Pull request #142: SCMI requirements - Pull request #148: Fix bibliography alignment for PDF and HTML - Pull request #149: chapter1: do not mention levels - Pull request #150: Clarify compatibility 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-nov-5-ahq7?lang=en #142: https://github.com/ARM-software/ebbr/pull/142 #148: https://github.com/ARM-software/ebbr/pull/148 #149: https://github.com/ARM-software/ebbr/pull/149 #150: https://github.com/ARM-software/ebbr/pull/150

3 weeks, 1 day

SMBIOS discovery for DT platforms booting without EFI

by Ard Biesheuvel

L.S., Adriana is proposing [0] a method for DT based platforms that boot without EFI to expose the SMBIOS tables via the /chosen DT node. There appears to be consensus between the stakeholders in the u-boot and linux communities that this is a reasonable thing to do, and it looks like this is going to be adopted soon. Adriana has kindly agreed to contributing the u-boot side implementation as well, so all the pieces will be there in terms of code. What is lacking is a contribution to the DMTF spec, which currently only permits the EFI config table method for non-x86 systems. So some wording should be added to paragraph 5.2.2 (SMBIOS 3.9 [1]) It currently reads On non-UEFI systems, the 64-bit SMBIOS Entry Point structure can be located by application software by searching for the anchor-string on paragraph (16-byte) boundaries within the physical memory address range 000F0000h to 000FFFFFh. Given that this makes sense only on x86 systems, I suggest we rephrase this along the lines of On non-UEFI systems, the 64-bit SMBIOS Entry Point structure can be located by application software - on x86 systems only, by searching for the anchor-string on paragraph (16-byte) boundaries within the physical memory address range 000F0000h to 000FFFFFh, - on DT based systems, by obtaining the physical memory address of the structure from the /chosen/smbios3-entrypoint property in the device tree. Maybe Rob can suggest a normative reference to be added to section 2? Thanks, Ard. [0] https://lore.kernel.org/all/CAERbo5z6BzHqQxXdxPxmxE_eDR7GGGbt3A8kB0gQiWFBE-… [1] https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.9.0.…

3 weeks, 3 days

Re: [PATCH v4 1/2] dt-bindings: firmware: Add binding for SMBIOS /chosen properties

by Rob Herring

On Fri, Oct 31, 2025 at 5:10 AM adriana <adriana(a)arista.com> wrote: > > Signed-off-by: adriana <adriana(a)arista.com> > --- > .../firmware/linux,smbios3-entrypoint.yaml | 25 +++++++++++++++++++ > 1 file changed, 25 insertions(+) > create mode 100644 Documentation/devicetree/bindings/firmware/linux,smbios3-entrypoint.yaml > > diff --git a/Documentation/devicetree/bindings/firmware/linux,smbios3-entrypoint.yaml b/Documentation/devicetree/bindings/firmware/linux,smbios3-entrypoint.yaml > new file mode 100644 > index 000000000000..4d1521c685ff > --- /dev/null > +++ b/Documentation/devicetree/bindings/firmware/linux,smbios3-entrypoint.yaml > @@ -0,0 +1,25 @@ > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) > +# Copyright 2025 Arista Networks > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/firmware/linux,smbios3-entrypoint.yaml# > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: Memory location for SMBIOS entry point > + > +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. > + > +maintainers: > + - Adriana Nicolae <adriana(a)arista.com> > + - Rob Herring <robh+dt(a)kernel.org> > + > +properties: > + linux,smbios3-entrypoint: > + $ref: /schemas/types.yaml#/definitions/uint64 > + description: > + The 64-bit physical address of the SMBIOSv3 entry point structure. This needs to go in the chosen binding instead: https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/chos…

3 weeks, 6 days

Re: [PATCH v4 0/2] DMI: Scan for DMI table from DTS info

by Ard Biesheuvel

On Fri, 31 Oct 2025 at 11:10, adriana <adriana(a)arista.com> 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. > > This series adds support for the kernel to find these tables by > reading the associated property from the Device Tree /chosen node. The > bootloader can specify the physical addresses using the property > "linux,smbios3-entrypoint". > > The first patch introduces the device tree binding documentation for this > new ABI, and the second patch implements the driver logic in dmi_scan.c. > > Changes in v4: > - Renamed linux,smbios3-table.yaml file, removed mention of ARM/ARM64 > (Patch 1/2). > - Drop the second definition of dmi_scan_from_dt() and fold checking > for CONFIG_OF (Patch 2/2). > - Drop unnecessary goto on the success case (Patch 2/2). > - Replace magic number for entrypoint size with SMBIOS3_ENTRY_POINT_SIZE > definition (Patch 2/2). > > Changes in v3: > - Removed linux,smbios-table property, only keep the SMBIOSv3 property > (Patch 1/2). > - Search DT for linux,smbios3-table only, removed the code searching > for the previous property (Patch 2/2). > > Changes in v2: > - Add missing Device Tree binding documentation (Patch 1/2). > - Split the original patch into a 2-part series (binding + driver). > - (No functional changes to the driver code in patch 2/2). > > adriana (2): > dt-bindings: firmware: Add binding for SMBIOS /chosen properties > drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT > For the series, Reviewed-by: Ard Biesheuvel <ardb(a)kernel.org> I can take the second patch, but bindings need to go in separately IIRC. Rob? > .../firmware/linux,smbios3-entrypoint.yaml | 25 +++++++++ > drivers/firmware/dmi_scan.c | 54 +++++++++++++++++++ > 2 files changed, 79 insertions(+) > create mode 100644 Documentation/devicetree/bindings/firmware/linux,smbios3-entrypoint.yaml > > -- > 2.51.0 >

3 weeks, 6 days

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

3 weeks, 6 days

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 >

3 weeks, 6 days

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 >

3 weeks, 6 days

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