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

From: Jonathan Cameron <[email-masked]>
Date: Fri, 7 Jun 2024 18:39:41 +0100

On Fri, 31 May 2024 16:38:38 -0500
Wei Huang <[email-masked]> 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 <[email-masked]>
> Signed-off-by: Eric Van Tassell <[email-masked]>
> Signed-off-by: Wei Huang <[email-masked]>
> Reviewed-by: Ajit Khaparde <[email-masked]>
> Reviewed-by: Somnath Kotur <[email-masked]> 
> Reviewed-by: Andy Gospodarek <[email-masked]>
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);