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

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Message-ID: <20251201174339.1852344-1-zhipingz@meta.com>
Date: Mon, 1 Dec 2025 09:43:20 -0800
From: Zhiping Zhang <zhipingz@...a.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
        Bjorn
 Helgaas <bhelgaas@...gle.com>, <linux-rdma@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <netdev@...r.kernel.org>,
        Keith Busch
	<kbusch@...nel.org>, Yochai Cohen <yochai@...dia.com>,
        Yishai Hadas
	<yishaih@...dia.com>
Subject: Re: [RFC 1/2] Set steering-tag directly for PCIe P2P memory access

> On Mon, 24 Nov 2025 15:27:53 -0600, Bjorn Helgaas wrote:
> > PCIe: Add a memory type for P2P memory access

> This should be in the Subject: line.

> It should also start with "PCI/TPH: ..." (not "PCIe") to match
> previous history.

Thanks, ack! I will update the subject line.

> > 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.

> s/tph/TPH/

> Make this say what the patch does (not just that we *need* another
> memory type, that we actually *add* one).

> The subject line should also say what the patch does.  I don't think
> this patch actually changes the *setting* of the steering tag (I could
> be wrong, I haven't looked carefully).

Sure, I’ll correct and revise the commit message to clearly state what the
patch does.

> > Signed-off-by: Zhiping Zhang <zhipingz@...a.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 */
> >  };
> >  
> >  #ifdef CONFIG_PCIE_TPH
> > -- 
> > 2.47.3
> >