Re: [RFC 1/2] Set steering-tag directly for PCIe P2P memory access

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

On Thu, 13 Nov 2025 13:37:11 -0800
Zhiping Zhang <zhipingz@meta.com> wrote:

> PCIe: Add a memory type for P2P memory access
> 
> The current tph memory type definition applies for CPU use cases. For device
> memory accessed in the peer-to-peer (P2P) manner, we need another memory
> type.
> 
> Signed-off-by: Zhiping Zhang <zhipingz@meta.com>
> ---
>  drivers/pci/tph.c       | 4 ++++
>  include/linux/pci-tph.h | 4 +++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
> index cc64f93709a4..d983c9778c72 100644
> --- a/drivers/pci/tph.c
> +++ b/drivers/pci/tph.c
> @@ -67,6 +67,8 @@ static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
>  			if (info->pm_st_valid)
>  				return info->pm_st;
>  			break;
> +		default:
> +			return 0;
>  		}
>  		break;
>  	case PCI_TPH_REQ_EXT_TPH: /* 16-bit tag */
> @@ -79,6 +81,8 @@ static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
>  			if (info->pm_xst_valid)
>  				return info->pm_xst;
>  			break;
> +		default:
> +			return 0;
>  		}
>  		break;
>  	default:
> diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
> index 9e4e331b1603..b989302b6755 100644
> --- a/include/linux/pci-tph.h
> +++ b/include/linux/pci-tph.h
> @@ -14,10 +14,12 @@
>   * 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.
> + * Add a new tph type for PCI peer-to-peer access use case.
>   */
>  enum tph_mem_type {
>  	TPH_MEM_TYPE_VM,	/* volatile memory */
> -	TPH_MEM_TYPE_PM		/* persistent memory */
> +	TPH_MEM_TYPE_PM,	/* persistent memory */
> +	TPH_MEM_TYPE_P2P	/* peer-to-peer accessable memory */

Trivial but this time definitely add the trailing comma!  Maybe there will never
be any more in here but maybe there will and we can avoid a line of
churn next time.

>  };
>  
>  #ifdef CONFIG_PCIE_TPH