RE: [RFC 1/1] of-fpga-region: Add sysfs interface support for FPGA configuration

Hi Yilun,

-----Original Message-----
From: Xu Yilun <redacted>
Sent: Monday, July 29, 2024 9:27 PM
To: Manne, Nava kishore <redacted>
Cc: git (AMD-Xilinx) <redacted>; mdf@kernel.org; hao.wu@intel.com;
yilun.xu@intel.com; trix@redhat.com; robh@kernel.org;
saravanak@google.com; linux-fpga@vger.kernel.org; linux-
kernel@vger.kernel.org; devicetree@vger.kernel.org
Subject: Re: [RFC 1/1] of-fpga-region: Add sysfs interface support for FPGA
configuration

On Fri, Jul 26, 2024 at 12:08:19PM +0530, Nava kishore Manne wrote:

quoted

Adds sysfs interface as part of the of-fpga-region. This newly added
sysfs interface uses Device Tree Overlay (DTO) files to
configure/reprogram an FPGA while an operating system is running.This
solution will not change the existing sequence When a DT overlay that
targets an FPGA Region is applied.
	- Disable appropriate FPGA bridges.
	- Program the FPGA using the FPGA manager.
	- Enable the FPGA bridges.
	- The Device Tree overlay is accepted into the live tree.
	- Child devices are populated.

When the overlay is removed, the child nodes will be removed, and the
FPGA Region will disable the bridges.

Usage:
To configure/reprogram an FPGA region:
echo "fpga.dtbo" > /sys/class/fpga_region/<region>/device/load

IIRC, last time we are considering some generic interface for both OF & non-
OF FPGA region, but this is still OF specific.

At AMD, we exclusively use OF for FPGA configuration/reconfiguration, utilizing overlay files as outlined in the fpga-region.txt documentation.
However, some devices, like dfl.c those relying solely on the FPGA region, do not use OF. 
For these non-OF devices, should we expect them to follow the fpga-region.txt guidelines for FPGA configuration/reconfiguration?
If so, it may be advantageous to develop a common interface for both OF and non-OF.
If not, it might be more appropriate to establish distinct interfaces to cater to their specific requirements.

Regards,
Navakishore.