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

[Manne, Nava kishore]

Hi Yilun,

> -----Original Message-----
> From: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> Sent: Monday, July 29, 2024 9:27 PM
> To: Manne, Nava kishore <nava.kishore.manne@xxxxxxx>
> Cc: git (AMD-Xilinx) <git@xxxxxxx>; mdf@xxxxxxxxxx; hao.wu@xxxxxxxxx;
> yilun.xu@xxxxxxxxx; trix@xxxxxxxxxx; robh@xxxxxxxxxx;
> saravanak@xxxxxxxxxx; linux-fpga@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx
> 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:
> > 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.