Re: [PATCH V4 08/12] PCI/TPH: Add pcie_tph_get_cpu_st() to get ST tag

[Alejandro Lucero Palau <alucerop@amd.com>]

On 8/22/24 21:41, Wei Huang wrote:
> Allow a caller to retrieve Steering Tags for a target memory that is
> associated with a specific CPU. The caller must provided two parameters,
> memory type and CPU UID, when calling this function. The tag is
> retrieved by invoking ACPI _DSM of the device's Root Port device.
>
> Co-developed-by: Eric Van Tassell <Eric.VanTassell@amd.com>
> Signed-off-by: Eric Van Tassell <Eric.VanTassell@amd.com>
> Signed-off-by: Wei Huang <wei.huang2@amd.com>
> Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
> Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
> Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
> ---
>   drivers/pci/pcie/tph.c  | 154 ++++++++++++++++++++++++++++++++++++++++
>   include/linux/pci-tph.h |  18 +++++
>   2 files changed, 172 insertions(+)
>
> diff --git a/drivers/pci/pcie/tph.c b/drivers/pci/pcie/tph.c
> index 82189361a2ee..5bd194fb425e 100644
> --- a/drivers/pci/pcie/tph.c
> +++ b/drivers/pci/pcie/tph.c
> @@ -7,12 +7,125 @@
>    *     Wei Huang <wei.huang2@amd.com>
>    */
>   #include <linux/pci.h>
> +#include <linux/pci-acpi.h>
>   #include <linux/bitfield.h>
>   #include <linux/msi.h>
>   #include <linux/pci-tph.h>
>   
>   #include "../pci.h"
>   
> +/*
> + * The st_info struct defines the Steering Tag (ST) info returned by the
> + * firmware _DSM method defined in the approved ECN for PCI Firmware Spec,
> + * available at https://members.pcisig.com/wg/PCI-SIG/document/15470.
> + *
> + * @vm_st_valid:  8-bit ST for volatile memory is valid
> + * @vm_xst_valid: 16-bit extended ST for volatile memory is valid
> + * @vm_ph_ignore: 1 => PH was and will be ignored, 0 => PH should be supplied
> + * @vm_st:        8-bit ST for volatile mem
> + * @vm_xst:       16-bit extended ST for volatile mem
> + * @pm_st_valid:  8-bit ST for persistent memory is valid
> + * @pm_xst_valid: 16-bit extended ST for persistent memory is valid
> + * @pm_ph_ignore: 1 => PH was and will be ignored, 0 => PH should be supplied
> + * @pm_st:        8-bit ST for persistent mem
> + * @pm_xst:       16-bit extended ST for persistent mem
> + */
> +union st_info {
> +	struct {
> +		u64 vm_st_valid : 1;
> +		u64 vm_xst_valid : 1;
> +		u64 vm_ph_ignore : 1;
> +		u64 rsvd1 : 5;
> +		u64 vm_st : 8;
> +		u64 vm_xst : 16;
> +		u64 pm_st_valid : 1;
> +		u64 pm_xst_valid : 1;
> +		u64 pm_ph_ignore : 1;
> +		u64 rsvd2 : 5;
> +		u64 pm_st : 8;
> +		u64 pm_xst : 16;
> +	};
> +	u64 value;
> +};
> +
> +static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
> +			   union st_info *info)
> +{
> +	switch (req_type) {
> +	case PCI_TPH_REQ_TPH_ONLY: /* 8-bit tag */
> +		switch (mem_type) {
> +		case TPH_MEM_TYPE_VM:
> +			if (info->vm_st_valid)
> +				return info->vm_st;
> +			break;
> +		case TPH_MEM_TYPE_PM:
> +			if (info->pm_st_valid)
> +				return info->pm_st;
> +			break;
> +		}
> +		break;
> +	case PCI_TPH_REQ_EXT_TPH: /* 16-bit tag */
> +		switch (mem_type) {
> +		case TPH_MEM_TYPE_VM:
> +			if (info->vm_xst_valid)
> +				return info->vm_xst;
> +			break;
> +		case TPH_MEM_TYPE_PM:
> +			if (info->pm_xst_valid)
> +				return info->pm_xst;
> +			break;
> +		}
> +		break;
> +	default:
> +		return 0;
> +	}
> +
> +	return 0;
> +}
> +
> +#define TPH_ST_DSM_FUNC_INDEX	0xF


Where is this coming from? Any spec to refer to?


> +static acpi_status tph_invoke_dsm(acpi_handle handle, u32 cpu_uid,
> +				  union st_info *st_out)
> +{
> +	union acpi_object arg3[3], in_obj, *out_obj;
> +
> +	if (!acpi_check_dsm(handle, &pci_acpi_dsm_guid, 7,


Again, what is this revision 7 based on? Specs?

I'm trying to use this patchset and this call fails. I've tried to use 
lower revision numbers with no success.

FWIW, I got no DSM function at all. This could be a problem with my BIOS 
or system, but in any case, this should be clearer specified in the code.


> +			    BIT(TPH_ST_DSM_FUNC_INDEX)))
> +		return AE_ERROR;
> +
> +	/* DWORD: feature ID (0 for processor cache ST query) */
> +	arg3[0].integer.type = ACPI_TYPE_INTEGER;
> +	arg3[0].integer.value = 0;
> +
> +	/* DWORD: target UID */
> +	arg3[1].integer.type = ACPI_TYPE_INTEGER;
> +	arg3[1].integer.value = cpu_uid;
> +
> +	/* QWORD: properties, all 0's */
> +	arg3[2].integer.type = ACPI_TYPE_INTEGER;
> +	arg3[2].integer.value = 0;
> +
> +	in_obj.type = ACPI_TYPE_PACKAGE;
> +	in_obj.package.count = ARRAY_SIZE(arg3);
> +	in_obj.package.elements = arg3;
> +
> +	out_obj = acpi_evaluate_dsm(handle, &pci_acpi_dsm_guid, 7,
> +				    TPH_ST_DSM_FUNC_INDEX, &in_obj);
> +	if (!out_obj)
> +		return AE_ERROR;
> +
> +	if (out_obj->type != ACPI_TYPE_BUFFER) {
> +		ACPI_FREE(out_obj);
> +		return AE_ERROR;
> +	}
> +
> +	st_out->value = *((u64 *)(out_obj->buffer.pointer));
> +
> +	ACPI_FREE(out_obj);
> +
> +	return AE_OK;
> +}
> +
>   /* Update the TPH Requester Enable field of TPH Control Register */
>   static void set_ctrl_reg_req_en(struct pci_dev *pdev, u8 req_type)
>   {
> @@ -140,6 +253,47 @@ static int write_tag_to_st_table(struct pci_dev *pdev, int index, u16 tag)
>   	return pci_write_config_word(pdev, offset, tag);
>   }
>   
> +/**
> + * pcie_tph_get_cpu_st() - Retrieve Steering Tag for a target memory associated
> + * with a specific CPU
> + * @pdev: PCI device
> + * @mem_type: target memory type (volatile or persistent RAM)
> + * @cpu_uid: associated CPU id
> + * @tag: Steering Tag to be returned
> + *
> + * This function returns the Steering Tag for a target memory that is
> + * associated with a specific CPU as indicated by cpu_uid.
> + *
> + * Returns 0 if success, otherwise negative value (-errno)
> + */
> +int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type mem_type,
> +			unsigned int cpu_uid, u16 *tag)
> +{
> +	struct pci_dev *rp;
> +	acpi_handle rp_acpi_handle;
> +	union st_info info;
> +
> +	rp = pcie_find_root_port(pdev);
> +	if (!rp || !rp->bus || !rp->bus->bridge)
> +		return -ENODEV;
> +
> +	rp_acpi_handle = ACPI_HANDLE(rp->bus->bridge);
> +
> +	if (tph_invoke_dsm(rp_acpi_handle, cpu_uid, &info) != AE_OK) {
> +		*tag = 0;
> +		return -EINVAL;
> +	}
> +
> +	*tag = tph_extract_tag(mem_type, pdev->tph_req_type, &info);
> +
> +	pci_dbg(pdev, "get steering tag: mem_type=%s, cpu_uid=%d, tag=%#04x\n",
> +		(mem_type == TPH_MEM_TYPE_VM) ? "volatile" : "persistent",
> +		cpu_uid, *tag);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(pcie_tph_get_cpu_st);
> +
>   /**
>    * pcie_tph_set_st_entry() - Set Steering Tag in the ST table entry
>    * @pdev: PCI device
> diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
> index a0c93b97090a..c9f33688b9a9 100644
> --- a/include/linux/pci-tph.h
> +++ b/include/linux/pci-tph.h
> @@ -9,9 +9,23 @@
>   #ifndef LINUX_PCI_TPH_H
>   #define LINUX_PCI_TPH_H
>   
> +/*
> + * According to the ECN for PCI Firmware Spec, Steering Tag can be different
> + * depending on the memory type: Volatile Memory or Persistent Memory. When a
> + * caller query about a target's Steering Tag, it must provide the target's
> + * tph_mem_type. ECN link: https://members.pcisig.com/wg/PCI-SIG/document/15470.
> + */
> +enum tph_mem_type {
> +	TPH_MEM_TYPE_VM,	/* volatile memory */
> +	TPH_MEM_TYPE_PM		/* persistent memory */
> +};
> +
>   #ifdef CONFIG_PCIE_TPH
>   int pcie_tph_set_st_entry(struct pci_dev *pdev,
>   			  unsigned int index, u16 tag);
> +int pcie_tph_get_cpu_st(struct pci_dev *dev,
> +			enum tph_mem_type mem_type,
> +			unsigned int cpu_uid, u16 *tag);
>   bool pcie_tph_enabled(struct pci_dev *pdev);
>   void pcie_disable_tph(struct pci_dev *pdev);
>   int pcie_enable_tph(struct pci_dev *pdev, int mode);
> @@ -20,6 +34,10 @@ int pcie_tph_modes(struct pci_dev *pdev);
>   static inline int pcie_tph_set_st_entry(struct pci_dev *pdev,
>   					unsigned int index, u16 tag)
>   { return -EINVAL; }
> +static inline int pcie_tph_get_cpu_st(struct pci_dev *dev,
> +				      enum tph_mem_type mem_type,
> +				      unsigned int cpu_uid, u16 *tag)
> +{ return -EINVAL; }
>   static inline bool pcie_tph_enabled(struct pci_dev *pdev) { return false; }
>   static inline void pcie_disable_tph(struct pci_dev *pdev) { }
>   static inline int pcie_enable_tph(struct pci_dev *pdev, int mode)