Subject: Re: [RFC] drivers/staging/axis-fifo: TODO file and subsystem direction

From: Greg KH <[email-masked]>
Date: Sun, 31 May 2026 17:25:10 +0200

On Sun, May 31, 2026 at 08:20:35PM +0530, Grewstad wrote:
> Dear Maintainers,
> 
> I am interested in contributing to the Xilinx AXI-Stream FIFO driver
> located in drivers/staging/axis-fifo.
> 
> While reviewing the driver, I noticed that it does not currently
> contain a TODO file describing the work required for graduation from
> staging. I would like to create such a file, but before doing so I
> would appreciate guidance on the expected long-term direction for the
> driver.
> 
> The driver currently exposes a custom userspace ABI through a
> miscdevice. While this provides a generic interface to the FIFO, it
> does not integrate with existing kernel subsystem tooling. One possible
> incremental improvement in this area could be a transition from
> miscdevice to a proper character device (cdev) interface, to allow for
> a more clearly defined and maintainable userspace ABI.

There really is no difference between a miscdevice and a character
device, the interaction from user/kernel is the same.

> Some possible directions that came to mind are:
> 
> - UIO, if the intent is to provide userspace control over a generic
>   AXI-stream FIFO with minimal kernel policy.

UIO provides a mmap of a device to userspace where it is controlled
directly.  Probably not what you want to do here right?

> - IIO, for data acquisition or SDR-oriented applications that could
>   benefit from existing buffer infrastructure and userspace tooling.

Is that what this device is?

> - Networking, for packet-oriented AXI-stream use cases.

WHat really is this device for?  What is the goal of this hardware and
how is it used today?  Do you have the hardware to test with it?  Who
uses it?

thanks,

greg k-h