Re: [PATCH 2/2] fpga: add FPGA manager debugfs

From: Moritz Fischer
Date: Thu Aug 16 2018 - 18:00:40 EST


Hi Federico,

On Thu, Aug 16, 2018 at 11:21:32PM +0200, Federico Vaga wrote:
> Hi,
>
> On Thursday, August 16, 2018 10:04:51 PM CEST Alan Tull wrote:
> > On Thu, Aug 16, 2018 at 1:59 PM, Moritz Fischer <mdf@xxxxxxxxxx> wrote:
> > > Hi Alan,
> >
> > Hi Moritz,
> >
> > > comments inline. While I see how this is useful, I have the
> > > suspicion that from the moment this gets merged vendor kernels
> > > will just default to use this ...
> >
> > Yeah, I have that suspicion as well. That's probably why I sat on
> > this and didn't upstream it for 2 years. But on the other hand, I
> > keep hearing of lots of cases of people implementing this
> > independently anyway. At least if it is debugfs, it makes it clear
> > that it's not intended for production use.
>
> I'm one of those guys who implemented this independently.

We all have in one way or another ;) Most people on ARM run an out of tree
patch using devicetree overlays these days I hope rather than /dev/mem
and UIO ... or other vender solutions...
>
> @Mortiz
> I do not see how this can be a bad thing (from what you wrote I guess you
> prefer another interface). Which interface to use depends on the use case.
> If you have this suspicion it's, I guess, because such interface it is
> extremely easy to use.

What happens to a kernel driver doing MMIO with devices while you reload
the entire FPGA from userland?
>
> @Alan
> DebugFS can be a first step, but I would go for a normal device in /dev at
> some point. I do not see why this should not be used in production

I'm not against having a userland interface to reprogram the FPGA, the
Intel DFL code is a good example of a sensible one, doing so in a safe
manner.

Ideally we'll get around to have a more generic interface, as we get
time to work on it.

- Moritz