Documentation/driver-api/cxl: device hotplug

[PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update

Posted by Gregory Price 1 month, 3 weeks ago

Add a snippet about what Linux expects BIOS/EFI to do (and not
to do) to the BIOS/EFI section.

Suggested-by: Alejandro Lucero Palau <alucerop@amd.com>
Signed-off-by: Gregory Price <gourry@gourry.net>
---
 .../driver-api/cxl/platform/bios-and-efi.rst  | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/driver-api/cxl/platform/bios-and-efi.rst b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
index a9aa0ccd92af..9034c206cf8e 100644
--- a/Documentation/driver-api/cxl/platform/bios-and-efi.rst
+++ b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
@@ -29,6 +29,26 @@ at :doc:`ACPI Tables <acpi>`.
    on physical memory region size and alignment, memory holes, HDM interleave,
    and what linux expects of HDM decoders trying to work with these features.
 
+
+Linux Expectations of BIOS/EFI Software
+=======================================
+Linux expects BIOS/EFI software to construct sufficient ACPI tables (such as
+CEDT, SRAT, HMAT, etc) and platform-specific configurations (such as HPA spaces
+and host-bridge interleave configurations) to allow the Linux driver to
+subsequently configure the devices in the CXL fabric at runtime.
+
+Programming of HDM decoders and switch ports is not required, and may be
+deferred to the CXL driver based on admin policy (e.g. udev rules).
+
+Some platforms may require pre-programming HDM decoders and locking them
+due to quirks (see: Zen5 address translation), but this is not the normal,
+"expected" configuration path.  This should be avoided if possible.
+
+Some platforms may wish to pre-configure these resources to bring memory
+up without requiring CXL driver support.  These platform vendors should
+test their configurations with the existing CXL driver and provide driver
+support for their auto-configurations if features like RAS are required.
+
 UEFI Settings
 =============
 If your platform supports it, the :code:`uefisettings` command can be used to
-- 
2.52.0

Re: [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update

Posted by Alejandro Lucero Palau 1 month, 3 weeks ago

On 12/19/25 17:05, Gregory Price wrote:
> Add a snippet about what Linux expects BIOS/EFI to do (and not
> to do) to the BIOS/EFI section.
>
> Suggested-by: Alejandro Lucero Palau <alucerop@amd.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>


Reviewed-by: Alejandro Lucero Palau <alucerop@amd.com>


> ---
>   .../driver-api/cxl/platform/bios-and-efi.rst  | 20 +++++++++++++++++++
>   1 file changed, 20 insertions(+)
>
> diff --git a/Documentation/driver-api/cxl/platform/bios-and-efi.rst b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> index a9aa0ccd92af..9034c206cf8e 100644
> --- a/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> +++ b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> @@ -29,6 +29,26 @@ at :doc:`ACPI Tables <acpi>`.
>      on physical memory region size and alignment, memory holes, HDM interleave,
>      and what linux expects of HDM decoders trying to work with these features.
>   
> +
> +Linux Expectations of BIOS/EFI Software
> +=======================================
> +Linux expects BIOS/EFI software to construct sufficient ACPI tables (such as
> +CEDT, SRAT, HMAT, etc) and platform-specific configurations (such as HPA spaces
> +and host-bridge interleave configurations) to allow the Linux driver to
> +subsequently configure the devices in the CXL fabric at runtime.
> +
> +Programming of HDM decoders and switch ports is not required, and may be
> +deferred to the CXL driver based on admin policy (e.g. udev rules).
> +
> +Some platforms may require pre-programming HDM decoders and locking them
> +due to quirks (see: Zen5 address translation), but this is not the normal,
> +"expected" configuration path.  This should be avoided if possible.
> +
> +Some platforms may wish to pre-configure these resources to bring memory
> +up without requiring CXL driver support.  These platform vendors should
> +test their configurations with the existing CXL driver and provide driver
> +support for their auto-configurations if features like RAS are required.
> +
>   UEFI Settings
>   =============
>   If your platform supports it, the :code:`uefisettings` command can be used to

Re: [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update

Posted by Dave Jiang 1 month ago


On 12/19/25 10:05 AM, Gregory Price wrote:
> Add a snippet about what Linux expects BIOS/EFI to do (and not
> to do) to the BIOS/EFI section.
> 
> Suggested-by: Alejandro Lucero Palau <alucerop@amd.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  .../driver-api/cxl/platform/bios-and-efi.rst  | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/driver-api/cxl/platform/bios-and-efi.rst b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> index a9aa0ccd92af..9034c206cf8e 100644
> --- a/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> +++ b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> @@ -29,6 +29,26 @@ at :doc:`ACPI Tables <acpi>`.
>     on physical memory region size and alignment, memory holes, HDM interleave,
>     and what linux expects of HDM decoders trying to work with these features.
>  
> +
> +Linux Expectations of BIOS/EFI Software
> +=======================================
> +Linux expects BIOS/EFI software to construct sufficient ACPI tables (such as
> +CEDT, SRAT, HMAT, etc) and platform-specific configurations (such as HPA spaces
> +and host-bridge interleave configurations) to allow the Linux driver to
> +subsequently configure the devices in the CXL fabric at runtime.
> +
> +Programming of HDM decoders and switch ports is not required, and may be
> +deferred to the CXL driver based on admin policy (e.g. udev rules).
> +
> +Some platforms may require pre-programming HDM decoders and locking them
> +due to quirks (see: Zen5 address translation), but this is not the normal,
> +"expected" configuration path.  This should be avoided if possible.
> +
> +Some platforms may wish to pre-configure these resources to bring memory
> +up without requiring CXL driver support.  These platform vendors should
> +test their configurations with the existing CXL driver and provide driver
> +support for their auto-configurations if features like RAS are required.
> +
>  UEFI Settings
>  =============
>  If your platform supports it, the :code:`uefisettings` command can be used to

Re: [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update

Posted by Jonathan Cameron 1 month, 3 weeks ago

On Fri, 19 Dec 2025 12:05:37 -0500
Gregory Price <gourry@gourry.net> wrote:

> Add a snippet about what Linux expects BIOS/EFI to do (and not
> to do) to the BIOS/EFI section.
> 
> Suggested-by: Alejandro Lucero Palau <alucerop@amd.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>

Nice.  Best of all I can blame you if our bios folk moan at me :)

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

> ---
>  .../driver-api/cxl/platform/bios-and-efi.rst  | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/driver-api/cxl/platform/bios-and-efi.rst b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> index a9aa0ccd92af..9034c206cf8e 100644
> --- a/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> +++ b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
> @@ -29,6 +29,26 @@ at :doc:`ACPI Tables <acpi>`.
>     on physical memory region size and alignment, memory holes, HDM interleave,
>     and what linux expects of HDM decoders trying to work with these features.
>  
> +
> +Linux Expectations of BIOS/EFI Software
> +=======================================
> +Linux expects BIOS/EFI software to construct sufficient ACPI tables (such as
> +CEDT, SRAT, HMAT, etc) and platform-specific configurations (such as HPA spaces
> +and host-bridge interleave configurations) to allow the Linux driver to
> +subsequently configure the devices in the CXL fabric at runtime.
> +
> +Programming of HDM decoders and switch ports is not required, and may be
> +deferred to the CXL driver based on admin policy (e.g. udev rules).
> +
> +Some platforms may require pre-programming HDM decoders and locking them
> +due to quirks (see: Zen5 address translation), but this is not the normal,
> +"expected" configuration path.  This should be avoided if possible.
> +
> +Some platforms may wish to pre-configure these resources to bring memory
> +up without requiring CXL driver support.  These platform vendors should
> +test their configurations with the existing CXL driver and provide driver
> +support for their auto-configurations if features like RAS are required.
> +
>  UEFI Settings
>  =============
>  If your platform supports it, the :code:`uefisettings` command can be used to

Re: [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update

Posted by Gregory Price 1 month, 3 weeks ago

On Fri, Dec 19, 2025 at 05:28:10PM +0000, Jonathan Cameron wrote:
> On Fri, 19 Dec 2025 12:05:37 -0500
> Gregory Price <gourry@gourry.net> wrote:
> 
> > Add a snippet about what Linux expects BIOS/EFI to do (and not
> > to do) to the BIOS/EFI section.
> > 
> > Suggested-by: Alejandro Lucero Palau <alucerop@amd.com>
> > Signed-off-by: Gregory Price <gourry@gourry.net>
> 
> Nice.  Best of all I can blame you if our bios folk moan at me :)
> 
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> 

:shrug:

"Patches Welcome" :]

~Gregory