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Subject: Re: [PATCH v3 1/2] Documentation: fpga: dfl: add PCI Identification
 documentation
To:     matthew.gerlach@linux.intel.com, hao.wu@intel.com,
        yilun.xu@intel.com, russell.h.weight@intel.com,
        basheer.ahmed.muddebihal@intel.com, mdf@kernel.org, corbet@lwn.net,
        linux-fpga@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, tianfei.zhang@intel.com
References: <20220707150549.265621-1-matthew.gerlach@linux.intel.com>
 <20220707150549.265621-2-matthew.gerlach@linux.intel.com>
From:   Tom Rix <trix@redhat.com>
Message-ID: <8180679b-1d71-a527-74f2-d77460ea9902@redhat.com>
Date:   Wed, 13 Jul 2022 15:07:12 -0700
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On 7/7/22 8:05 AM, matthew.gerlach@linux.intel.com wrote:
> From: Matthew Gerlach <matthew.gerlach@linux.intel.com>
>
> Add documentation on identifying FPGA based PCI cards prompted
> by discussion on the linux-fpga@vger.kernel.org mailing list.
>
> Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
> ---
> v3: Add url to page tracking PCI ID information for DFL based cards.
>
> v2: Introduced in v2.
> ---
>   Documentation/fpga/dfl.rst | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
>
> diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst
> index 15b670926084..5144775b860a 100644
> --- a/Documentation/fpga/dfl.rst
> +++ b/Documentation/fpga/dfl.rst
> @@ -507,6 +507,27 @@ ids application.
>   https://github.com/OPAE/dfl-feature-id
>   
>   
> +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. Further PCI Product, Vendor, and Subsystem id tracking
> +can be found at https://github.com/OPAE/dfl-feature-id/blob/main/dfl-pci-ids.rst.

This link looks good.

It may be good to be explicit and say which device(s) needs to be 
specified by the quadruple.

Reviewed-by: Tom Rix <trix@redhat.com>

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