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

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Date:   Fri, 11 Mar 2022 04:16:51 +0000
From:   "Wu, Hao" <hao.wu@...el.com>
To:     "matthew.gerlach@...ux.intel.com" <matthew.gerlach@...ux.intel.com>,
        "Xu, Yilun" <yilun.xu@...el.com>,
        "Weight, Russell H" <russell.h.weight@...el.com>,
        "Muddebihal, Basheer Ahmed" <basheer.ahmed.muddebihal@...el.com>,
        "trix@...hat.com" <trix@...hat.com>,
        "mdf@...nel.org" <mdf@...nel.org>,
        "corbet@....net" <corbet@....net>,
        "linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Zhang, Tianfei" <tianfei.zhang@...el.com>
Subject: RE: [PATCH v2 1/2] Documentation: fpga: dfl: add PCI Identification
 documentation

> Subject: [PATCH v2 1/2] Documentation: fpga: dfl: add PCI Identification
> documentation
> 
> 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.

I think PCI Device/Card Identification is out of scope of DFL. DFL is another
level concept, it can't help to identify which card it is. There is no additional
requirement to users, they can choose any method they want, and they 
don't have to reuse dfl-pci for their own cards.

> +
>  Location of DFLs on a PCI Device
>  ================================
>  The original method for finding a DFL on a PCI device assumed the start of the
> --
> 2.25.1