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

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Date:   Thu, 3 Mar 2022 14:04:00 -0800
From:   Tom Rix <trix@...hat.com>
To:     matthew.gerlach@...ux.intel.com, hao.wu@...el.com,
        yilun.xu@...el.com, russell.h.weight@...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 3/2/22 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 ?

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