netdev - Re: [PATCH V7 5/9] PCI/IOV: Enable 10-Bit tag support for PCIe VF devices

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Message-ID: <20210806225917.GA1897594@bjorn-Precision-5520>
Date:   Fri, 6 Aug 2021 17:59:17 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Dongdong Liu <liudongdong3@...wei.com>
Cc:     hch@...radead.org, kw@...ux.com, logang@...tatee.com,
        leon@...nel.org, linux-pci@...r.kernel.org, rajur@...lsio.com,
        hverkuil-cisco@...all.nl, linux-media@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH V7 5/9] PCI/IOV: Enable 10-Bit tag support for PCIe VF
 devices

On Thu, Aug 05, 2021 at 04:03:58PM +0800, Dongdong Liu wrote:
> 
> On 2021/8/5 7:29, Bjorn Helgaas wrote:
> > On Wed, Aug 04, 2021 at 09:47:04PM +0800, Dongdong Liu wrote:
> > > Enable VF 10-Bit Tag Requester when it's upstream component support
> > > 10-bit Tag Completer.
> > 
> > I think "upstream component" here means the PF, doesn't it?  I don't
> > think the PF is really an *upstream* component; there's no routing
> > like with a switch.
>
> I want to say the switch and root port devices that support 10-Bit
> Tag Completer. Sure, VF also needs to have 10-bit Tag Requester
> Supported capability.

OK.  IIUC we're not talking about P2PDMA here; we're talking about
regular DMA to host memory, which means I *think* only the Root Port
is important, since it is the completer for DMA to host memory.  We're
not talking about P2PDMA to a switch BAR, where the switch would be
the completer.