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

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Message-ID: <fee2f889-f549-26a1-4afa-57f52500d6e2@deltatee.com>
Date:   Thu, 5 Aug 2021 09:36:55 -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 2021-08-05 7:14 a.m., Dongdong Liu wrote:
> On 2021/8/4 23:51, Logan Gunthorpe wrote:
>>
>>
>>
>> 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.
> Does the command line parameter as "[PATCH V6 7/8] PCI: Add
> "pci=disable_10bit_tag=" parameter for peer-to-peer support" does?
> 
> Do we also need such command line if we already had sysfs file?
> I think we may not need.

In my opinion, for reasons stated above, the command line parameter is
way more convenient.

Logan