Hi Yilun,

	Please find my response inline.

-----Original Message-----
From: Xu Yilun <redacted>
Sent: Monday, January 8, 2024 12:02 PM
To: Manne, Nava kishore <redacted>
Cc: mdf@kernel.org; hao.wu@intel.com; yilun.xu@intel.com;
trix@redhat.com; peter.colberg@intel.com; conor.dooley@microchip.com;
v.georgiev@metrotek.ru; Simek, Michal [off-list ref]; Marco
Pagani [off-list ref]; gregkh@linuxfoundation.org;
ruanjinjie@huawei.com; linux-fpga@vger.kernel.org; linux-
kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; git (AMD-Xilinx)
[off-list ref]
Subject: Re: [RFC] FPGA Subsystem User Space Interface Proposal

On Thu, Jan 04, 2024 at 04:52:15AM +0000, Manne, Nava kishore wrote:

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================================================================
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=
| Introduction                                                        |

================================================================
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= This document provides a detailed overview of the proposed Kernel
feature for FPGA Manager subsystem user interface.
It describes the problem statement behind the proposal, the problem to be

solved, a top-level solution design.

quoted

Table of Contents:
------------------
A. Problem Statement and Background
B. Scope and Out of scope of the proposal
     B.1 Scope
     B.2 Out of scope
C. Proposed Solution
D. Proposed User Interface Details

================================================================
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=
| A. Problem Statement and Background                                        |

================================================================
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= The existing FPGA manager subsystem didn't have any user space
interface (other than the status/state in sysfs) in Kernel.
Basically, FPGAs are semiconductor devices that can be reprogrammed for

desired hardware functionality.

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FPGAs can be reprogrammed at runtime with different types of logic and IPs

as per user need and hence there is a need to use device tree overlays for
removing/updating/adding the devices at runtime for the IPs/controllers that
are present in FPGA.

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But we don't have any user interface in kernel for updating the device tree

at runtime.

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Sometime back there was a series sent by Pantelis Antoniou

(https://lore.kernel.org/lkml/1414528565-10907-4-git-send-email-
pantelis.antoniou@konsulko.com/).

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This patch introduced a user interface configfs for Device Tree overlays, a

method of dynamically altering the kernel's live Device Tree. However,  this
patch series was not accepted in mainline due to various concerns.

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For more details refer to this link:

https://elinux.org/Frank%27s_Evolving_Overlay_Thoughts#issues_and_what

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_needs_to_be_completed_--_Not_an_exhaustive_list

One of the major valid concerns that were raised with this configfs interface

was security as it opens up the interface to users for modifying the live device
tree.

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So, in order to configure/program the FPGA devices, All the major
vendors of FPGA are using this configfs series as out-of-tree patch for

configuring the FPGAs and there was never an attempt to introduce a generic
interface to configure/program the FPGA in upstream and hence upstream
kernel ended up in not having proper support for FPGAs.

quoted

The proposal below tries to address this gap of FPGA programmability by

providing an interface to the user.

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================================================================
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=
| B. Proposed Solution                                                |

================================================================
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= The proposed interface adds a new sysfs interface (of-fpga-region.c)
as part of the fpga subsystem and it is responsible for supporting the below

functionalities.

Why only for of-fpga-region? There are also FPGA regions that don't rely on
OF. My quick idea is that an interface for /sys/class/fpga-region/ and OF could
be one of the implementation.

I agree, few devices(Like - dfl-fme-region.c) are rely only on FPGA region and they are not using OF. Thanks for pointing out this case.
I will look at the possibility of having a generic interface for both Fpga region and OF and I will get back to you soon.

Regards,
Navakishore.

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