Re: [PATCH v3 11/11] cxl: Enable AMD Zen5 address translation using ACPI PRMT

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Fri, 12 Sep 2025 16:45:13 +0200
Robert Richter <rrichter@amd.com> wrote:

> Add AMD Zen5 support for address translation.
> 
> Zen5 systems may be configured to use 'Normalized addresses'. Then,
> CXL endpoints use their own physical address space and are programmed
> passthrough (DPA == HPA), the number of interleaving ways for the
> endpoint is set to one. The Host Physical Addresses (HPAs) need to be
> translated from the endpoint to its CXL host bridge. The HPA of a CXL
> host bridge is equivalent to the System Physical Address (SPA).
> 
> ACPI Platform Runtime Mechanism (PRM) is used to translate the CXL
> Device Physical Address (DPA) to its System Physical Address. This is
> documented in:
> 
>  AMD Family 1Ah Models 00h–0Fh and Models 10h–1Fh
>  ACPI v6.5 Porting Guide, Publication # 58088
>  https://www.amd.com/en/search/documentation/hub.html
> 
> To implement AMD Zen5 address translation the following steps are
> needed:
> 
> AMD Zen5 systems support the ACPI PRM CXL Address Translation firmware
> call (Address Translation - CXL DPA to System Physical Address, see
> ACPI v6.5 Porting Guide above) when address translation is enabled.
> The existence of the callback can be identified using a specific GUID
> as documented. The initialization code checks firmware and kernel
> support of ACPI PRM.
> 
> Introduce a new file core/atl.c to handle ACPI PRM specific address
> translation code. Naming is loosely related to the kernel's AMD
> Address Translation Library (CONFIG_AMD_ATL) but implementation does
> not dependent on it, nor it is vendor specific. Use Kbuild and Kconfig
> options respectively to enable the code depending on architecture and
> platform options.
> 
> Implement an ACPI PRM firmware call for CXL address translation in the
> new function cxl_prm_to_hpa(). This includes sanity checks. Enable the
> callback for applicable CXL host bridges using the new cxl_atl_init()
> function.
> 
> Signed-off-by: Robert Richter <rrichter@amd.com>
A few minor additions inline.  

J
> ---
>  drivers/cxl/Kconfig       |   4 ++
>  drivers/cxl/core/Makefile |   1 +
>  drivers/cxl/core/atl.c    | 138 ++++++++++++++++++++++++++++++++++++++
>  drivers/cxl/core/core.h   |   1 +
>  drivers/cxl/core/port.c   |   8 +++
>  5 files changed, 152 insertions(+)
>  create mode 100644 drivers/cxl/core/atl.c
> 
> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index 48b7314afdb8..31f9c96ef908 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -233,4 +233,8 @@ config CXL_MCE
>  	def_bool y
>  	depends on X86_MCE && MEMORY_FAILURE
>  
> +config CXL_ATL
> +       def_bool y

Given no help we can't turn this off manually and it's down to
whether ACPI_PRMT is configured or not.

To me this feels like something we should be able to control.
Not a huge amount of code, but none the less 'so far' it only
applies to particular AMD platforms yet ACPI_PRMT gets built
on ARM platforms and other stuff even on AMD (CONFIG_AMD_ATL_PRM)



> +       depends on ACPI_PRMT
> +
>  endif

> diff --git a/drivers/cxl/core/atl.c b/drivers/cxl/core/atl.c
> new file mode 100644
> index 000000000000..5fc21eddaade
> --- /dev/null
> +++ b/drivers/cxl/core/atl.c

> +struct prm_cxl_dpa_spa_data {
> +	u64 dpa;
> +	u8 reserved;
> +	u8 devfn;
> +	u8 bus;
> +	u8 segment;
> +	void *out;

If reality is out is always a u64 * maybe just give it that type.

> +} __packed;
> +
> +static u64 prm_cxl_dpa_spa(struct pci_dev *pci_dev, u64 dpa)
> +{
> +	struct prm_cxl_dpa_spa_data data;
> +	u64 spa;
> +	int rc;
> +
> +	data = (struct prm_cxl_dpa_spa_data) {
> +		.dpa     = dpa,
> +		.devfn   = pci_dev->devfn,
> +		.bus     = pci_dev->bus->number,
> +		.segment = pci_domain_nr(pci_dev->bus),
> +		.out     = &spa,
> +	};
> +
> +	rc = acpi_call_prm_handler(prm_cxl_dpa_spa_guid, &data);
> +	if (rc) {
> +		pci_dbg(pci_dev, "failed to get SPA for %#llx: %d\n", dpa, rc);
> +		return ULLONG_MAX;
> +	}
> +
> +	pci_dbg(pci_dev, "PRM address translation: DPA -> SPA: %#llx -> %#llx\n", dpa, spa);
> +
> +	return spa;
> +}
> +
> +static u64 cxl_prm_to_hpa(struct cxl_decoder *cxld, u64 hpa)
> +{

> +	pci_dev = to_pci_dev(cxlmd->dev.parent);


	return prm_cxl_dpa_spa(to_pci_dev(cxlmd->dev.parent), hpa);
seem fine to me and shortens things a little.

> +
> +	return prm_cxl_dpa_spa(pci_dev, hpa);
> +}
> +
> +static void cxl_prm_init(struct cxl_port *port)
> +{
> +	u64 spa;
> +	struct prm_cxl_dpa_spa_data data = { .out = &spa, };
> +	int rc;
> +
> +	if (!check_prm_address_translation(port))
> +		return;
> +
> +	/* Check kernel (-EOPNOTSUPP) and firmware support (-ENODEV) */
> +	rc = acpi_call_prm_handler(prm_cxl_dpa_spa_guid, &data);
> +	if (rc == -EOPNOTSUPP || rc == -ENODEV)
> +		return;

So other error values are fine?  IF they don't occur no need to be explicit
just check rc < 0 and return.

> +
> +	port->to_hpa = cxl_prm_to_hpa;
> +
> +	dev_dbg(port->host_bridge, "PRM address translation enabled for %s.\n",
> +		dev_name(&port->dev));
> +}
> +
> +void cxl_atl_init(struct cxl_port *port)
> +{
> +	cxl_prm_init(port);
Why not just rename cxl_prm_init() to cxl_atl_init() and get rid of this wrapper?

> +}