linux-kernel - Re: [PATCH 02/16] fpga: add FPGA device framework

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Date:   Fri, 31 Mar 2017 08:09:09 +0200
From:   Greg KH <greg@...ah.com>
To:     Wu Hao <hao.wu@...el.com>
Cc:     atull@...nel.org, moritz.fischer@...us.com,
        linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org,
        luwei.kang@...el.com, yi.z.zhang@...el.com,
        Tim Whisonant <tim.whisonant@...el.com>,
        Enno Luebbers <enno.luebbers@...el.com>,
        Shiva Rao <shiva.rao@...el.com>,
        Christopher Rauer <christopher.rauer@...el.com>,
        Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Subject: Re: [PATCH 02/16] fpga: add FPGA device framework

On Thu, Mar 30, 2017 at 08:08:02PM +0800, Wu Hao wrote:
> During FPGA device (e.g PCI-based) discovery, platform devices are
> registered for different FPGA function units. But the device node path
> isn't quite friendly to applications.
> 
> Consider this case, applications want to access child device's sysfs file
> for some information.
> 
> 1) Access using bus-based path (e.g PCI)
> 
>   /sys/bus/pci/devices/xxxxx/fpga_func_a.0/sysfs_file
> 
>   From the path, it's clear which PCI device is the parent, but not perfect
>   solution for applications. PCI device BDF is not fixed, application may
>   need to search all PCI device to find the actual FPGA Device.
> 
> 2) Or access using platform device path
> 
>   /sys/bus/platform/devices/fpga_func_a.0/sysfs_file
> 
>   Applications find the actual function by name easily, but no information
>   about which fpga device it belongs to. It's quite confusing if multiple
>   FPGA devices are in one system.
> 
> 'FPGA Device' class is introduced to resolve this problem. Each node under
> this class represents a fpga device, which may have one or more child
> devices. Applications only need to search under this FPGA Device class
> folder to find the child device node it needs.
> 
> For example, for the platform has 2 fpga devices, each fpga device has
> 3 child devices, the hierarchy looks like this.
> 
> Two nodes are under /sys/class/fpga/:
> /sys/class/fpga/fpga.0
> /sys/class/fpga/fpga.1
> 
> Each node has 1 function A device and 2 function B devices:
> /sys/class/fpga/fpga.0/func_a.0
> /sys/class/fpga/fpga.0/func_b.0
> /sys/class/fpga/fpga.0/func_b.1
> 
> /sys/class/fpga/fpga.1/func_a.1
> /sys/class/fpga/fpga.1/func_b.2
> /sys/class/fpga/fpga.1/func_b.3
> 
> This following APIs are provided by FPGA device framework:
> * fpga_dev_create
>   Create fpga device under the given parent device.
> * fpga_dev_destroy
>   Destroy fpga device
> 
> The following sysfs files are created:
> * /sys/class/fpga/<fpga.x>/name
>   Name of the fpga device.

How does this interact with the existing "fpga class" that is in the
kernel already?

thanks,

greg k-h