Re: [PATCH V2 6/9] PCI/TPH: Retrieve steering tag from ACPI _DSM

Jonathan Cameron
2024-06-07T17:39:45Z

On Fri, 31 May 2024 16:38:38 -0500
Wei Huang <wei.huang2@amd.com> wrote:

> According to PCI SIG ECN, calling the _DSM firmware method for a given
> CPU_UID returns the steering tags for different types of memory
> (volatile, non-volatile). These tags are supposed to be used in ST
> table entry for optimal results.
>
> 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>
Took a very quick look at this only due to lack of time..

> ---
> drivers/pci/pcie/tph.c | 103 +++++++++++++++++++++++++++++++++++++++-
> include/linux/pci-tph.h | 34 +++++++++++++
> 2 files changed, 136 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pcie/tph.c b/drivers/pci/pcie/tph.c
> index 320b99c60365..425935a14b62 100644
> --- a/drivers/pci/pcie/tph.c
> +++ b/drivers/pci/pcie/tph.c
> @@ -158,6 +158,98 @@ static int tph_get_table_location(struct pci_dev *dev, u8 *loc_out)
> return 0;
> }
>
> +static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
> + union st_info *st_tag)
> +{
> + switch (req_type) {
> + case PCI_TPH_REQ_TPH_ONLY: /* 8 bit tags */
> + switch (mem_type) {
> + case TPH_MEM_TYPE_VM:
> + if (st_tag->vm_st_valid)
> + return st_tag->vm_st;
> + break;
> + case TPH_MEM_TYPE_PM:
> + if (st_tag->pm_st_valid)
> + return st_tag->pm_st;
> + break;
> + }
> + break;
> + case PCI_TPH_REQ_EXT_TPH: /* 16 bit tags */
> + switch (mem_type) {
> + case TPH_MEM_TYPE_VM:
> + if (st_tag->vm_xst_valid)
> + return st_tag->vm_xst;
> + break;
> + case TPH_MEM_TYPE_PM:
> + if (st_tag->pm_xst_valid)
> + return st_tag->pm_xst;
> + break;
> + }
> + break;
> + default:
> + pr_err("invalid steering tag in ACPI _DSM\n");
> + return 0;
Not an error code? If so need to explain why 0 is the right thing to
return.
> + }
> +
> + return 0;
> +}
> +
> +#define MIN_ST_DSM_REV 7
> +#define ST_DSM_FUNC_INDEX 0xf
> +static bool invoke_dsm(acpi_handle handle, u32 cpu_uid, u8 ph,

give that a pci / tph prefix of some type as it's a very generic
name so potential future name clashes likely.

> + u8 target_type, bool cache_ref_valid,
> + u64 cache_ref, union st_info *st_out)
> +{
> + union acpi_object in_obj, in_buf[3], *out_obj;

I'm out of time for the day, so not checked this. Will look more
closely in v3.

> +
> + in_buf[0].integer.type = ACPI_TYPE_INTEGER;
> + in_buf[0].integer.value = 0; /* 0 => processor cache steering tags */
> +
> + in_buf[1].integer.type = ACPI_TYPE_INTEGER;
> + in_buf[1].integer.value = cpu_uid;
> +
> + in_buf[2].integer.type = ACPI_TYPE_INTEGER;
> + in_buf[2].integer.value = ph & 3;
> + in_buf[2].integer.value |= (target_type & 1) << 2;
> + in_buf[2].integer.value |= (cache_ref_valid & 1) << 3;
> + in_buf[2].integer.value |= (cache_ref << 32);
> +
> + in_obj.type = ACPI_TYPE_PACKAGE;
> + in_obj.package.count = ARRAY_SIZE(in_buf);
> + in_obj.package.elements = in_buf;
> +
> + out_obj = acpi_evaluate_dsm(handle, &pci_acpi_dsm_guid, MIN_ST_DSM_REV,
> + ST_DSM_FUNC_INDEX, &in_obj);
> +
> + if (!out_obj)
> + return false;
> +
> + if (out_obj->type != ACPI_TYPE_BUFFER) {
> + pr_err("invalid return type %d from TPH _DSM\n",
> + out_obj->type);
> + ACPI_FREE(out_obj);
> + return false;
> + }
> +
> + st_out->value = *((u64 *)(out_obj->buffer.pointer));
> +
> + ACPI_FREE(out_obj);
> +
> + return true;
> +}
> +

> static bool msix_nr_in_bounds(struct pci_dev *dev, int msix_nr)
> {
> u16 tbl_sz;
> @@ -441,7 +533,16 @@ bool pcie_tph_get_st(struct pci_dev *dev, unsigned int cpu,
> enum tph_mem_type mem_type, u8 req_type,
> u16 *tag)
Add this function in this patch as it's not used before here and all
the logic is about the _DSM
Note name needs to change though.

> {
> - *tag = 0;
> + union st_info info;
> +
> + if (!invoke_dsm(root_complex_acpi_handle(dev), cpu, 0, 0, false, 0,
> + &info)) {
> + *tag = 0;
> + return false;
> + }
> +
> + *tag = tph_extract_tag(mem_type, req_type, &info);
> + pr_debug("%s: cpu=%d tag=%d\n", __func__, cpu, *tag);
>
> return true;
> }
> diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
> index 4fbd1e2fd98c..79533c6254c2 100644
> --- a/include/linux/pci-tph.h
> +++ b/include/linux/pci-tph.h
> @@ -14,6 +14,40 @@ enum tph_mem_type {
> TPH_MEM_TYPE_PM /* persistent memory type */
> };
>
> +/*
> + * The st_info struct defines the steering tag returned by the firmware _DSM
> + * method defined in PCI SIG ECN. The specification is available at:
> + * https://members.pcisig.com/wg/PCI-SIG/document/15470.
> +
> + * @vm_st_valid: 8 bit tag for volatile memory is valid
> + * @vm_xst_valid: 16 bit tag for volatile memory is valid
> + * @vm_ignore: 1 => was and will be ignored, 0 => ph should be supplied
> + * @vm_st: 8 bit steering tag for volatile mem
> + * @vm_xst: 16 bit steering tag for volatile mem
> + * @pm_st_valid: 8 bit tag for persistent memory is valid
> + * @pm_xst_valid: 16 bit tag for persistent memory is valid
> + * @pm_ignore: 1 => was and will be ignore, 0 => ph should be supplied
pm_ph_ignore

> + * @pm_st: 8 bit steering tag for persistent mem
> + * @pm_xst: 16 bit steering tag for persistent mem
> + */
> +union st_info {
> + struct {
> + u64 vm_st_valid:1,
> + vm_xst_valid:1,
> + vm_ph_ignore:1,
> + rsvd1:5,
> + vm_st:8,
> + vm_xst:16,
> + pm_st_valid:1,
> + pm_xst_valid:1,
> + pm_ph_ignore:1,
> + rsvd2:5,
> + pm_st:8,
> + pm_xst:16;
> + };
> + u64 value;
> +};
Firstly why in a header? If it did want to be then pci-acpi.h might be reasonable.

> +
> #ifdef CONFIG_PCIE_TPH
> int pcie_tph_disable(struct pci_dev *dev);
> int tph_set_dev_nostmode(struct pci_dev *dev);