netdev - Re: [PATCH V7 7/9] PCI/sysfs: Add a 10-Bit Tag sysfs file

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Date:   Wed, 4 Aug 2021 09:51:29 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Dongdong Liu <liudongdong3@...wei.com>, helgaas@...nel.org,
        hch@...radead.org, kw@...ux.com, leon@...nel.org,
        linux-pci@...r.kernel.org, rajur@...lsio.com,
        hverkuil-cisco@...all.nl
Cc:     linux-media@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH V7 7/9] PCI/sysfs: Add a 10-Bit Tag sysfs file




On 2021-08-04 7:47 a.m., Dongdong Liu wrote:
> PCIe spec 5.0 r1.0 section 2.2.6.2 says that if an Endpoint supports
> sending Requests to other Endpoints (as opposed to host memory), the
> Endpoint must not send 10-Bit Tag Requests to another given Endpoint
> unless an implementation-specific mechanism determines that the Endpoint
> supports 10-Bit Tag Completer capability. Add a 10bit_tag sysfs file,
> write 0 to disable 10-Bit Tag Requester when the driver does not bind
> the device if the peer device does not support the 10-Bit Tag Completer.
> This will make P2P traffic safe. the 10bit_tag file content indicate
> current 10-Bit Tag Requester Enable status.

Can we not have both the sysfs file and the command line parameter? If
the user wants to disable it always for a specific device this sysfs
parameter is fairly awkward. A script at boot to unbind the driver, set
the sysfs file and rebind the driver is not trivial and the command line
parameter offers additional options for users.

Logan