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

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Date:   Fri, 4 Mar 2022 08:45:20 -0800
From:   Russ Weight <russell.h.weight@...el.com>
To:     Tom Rix <trix@...hat.com>, <matthew.gerlach@...ux.intel.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 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.
>
> Why couldn't one of the old pci id's be reused ?
>
> How will the subvendor/subid be enforced ?
>
> 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 ?
>
> Tom
>
>> +
>>   Location of DFLs on a PCI Device
>>   ================================
>>   The original method for finding a DFL on a PCI device assumed the start of the
>