linux-kernel - Re: [PATCH v2 1/2] Documentation: fpga: dfl: add PCI Identification documentation

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Message-ID: <alpine.DEB.2.22.394.2203041021240.3408681@rhweight-WRK1>
Date:   Fri, 4 Mar 2022 10:30:47 -0800 (PST)
From:   matthew.gerlach@...ux.intel.com
To:     Russ Weight <russell.h.weight@...el.com>
cc:     Tom Rix <trix@...hat.com>, hao.wu@...el.com, yilun.xu@...el.com,
        basheer.ahmed.muddebihal@...el.com, mdf@...nel.org, corbet@....net,
        linux-fpga@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, dan.j.williams@...el.com,
        ashok.raj@...el.com, tianfei.zhang@...el.com
Subject: Re: [PATCH v2 1/2] Documentation: fpga: dfl: add PCI Identification
 documentation



On Fri, 4 Mar 2022, Russ Weight wrote:

>
>
> On 3/3/22 14:04, Tom Rix wrote:
>>
>> On 3/2/22 4:35 PM, matthew.gerlach@...ux.intel.com wrote:
>>> From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>>>
>>> Add documentation on identifying FPGA based PCI cards prompted
>>> by discussion on the linux-fpga@...r.kernel.org mailing list.
>>>
>>> Signed-off-by: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>>> ---
>>> v2: Introduced in v2.
>>> ---
>>>   Documentation/fpga/dfl.rst | 20 ++++++++++++++++++++
>>>   1 file changed, 20 insertions(+)
>>>
>>> diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst
>>> index ef9eec71f6f3..5fb2ca8e76d7 100644
>>> --- a/Documentation/fpga/dfl.rst
>>> +++ b/Documentation/fpga/dfl.rst
>>> @@ -502,6 +502,26 @@ Developer only needs to provide a sub feature driver with matched feature id.
>>>   FME Partial Reconfiguration Sub Feature driver (see drivers/fpga/dfl-fme-pr.c)
>>>   could be a reference.
>>>   +PCI Device Identification
>>> +================================
>>> +Since FPGA based PCI cards can be reconfigured to a perform a completely
>>> +new function at runtime, properly identifying such cards and binding the
>>> +correct driver can be challenging. In many use cases, deployed FPGA based
>>> +PCI cards are essentially static and the PCI Product ID and Vendor ID pair
>>> +is sufficient to identify the card.  The DFL framework helps with the
>>> +dynamic case of deployed FPGA cards changing at run time by providing
>>> +more detailed information about card discoverable at runtime.
>>> +
>>> +At one level, the DFL on a PCI card describes the function of the card.
>>> +However, the same DFL could be instantiated on different physical cards.
>>> +Conversely, different DFLs could be instantiated on the same physical card.
>>> +Practical management of a cloud containing a heterogeneous set of such cards
>>> +requires a PCI level of card identification. While the PCI Product ID and
>>> +Vendor ID may be sufficient to bind the dfl-pci driver, it is expected
>>> +that FPGA PCI cards would advertise suitable Subsystem ID and Subsystem
>>> +Vendor ID values. PCI Vital Product Data (VPD) can also be used for
>>> +more granular information about the board.
>>
>> This describes a bit more of the problem, it should describe it wrt ofs dev id. The introduction of the ofs dev should be explicitly called out as a generic pci id.

The problem I'm describing exists for all FPGA based PCI cards; so I am 
purposely trying to be abstract as much as possible.

>>
>> Why couldn't one of the old pci id's be reused ?

Yes, old pci id's could be reused, and people have done just that.  We 
thought a new PCI ID would minimize confusion with cards that have already 
been deployed.

>>
>> How will the subvendor/subid be enforced ?

Subvendor and Subid are managed just like any other PCI card with or 
without a FPGA.

>>
>> Is the current security manager patchset smart enough to save the board from being bricked when a user doesn't look beyond the pci id ?
>
> Yes - the security manager is invoked based of DFL feature ID and revision, and the functionality is differentiated based on the same information.
>
>>
>> What happens if a board uses this device id but doesn't have a max10 to do the update ?

If a board doesn't have a max10, then there will be no DFH for a max10 in 
the board's DFLs.  Presumeably, the board would need some update process, 
and an approprate DFH would be in that board's DFL.

>>
>> Tom
>>
>>> +
>>>   Location of DFLs on a PCI Device
>>>   ================================
>>>   The original method for finding a DFL on a PCI device assumed the start of the
>>
>
>