Hi,

On Friday, August 17, 2018 5:22:56 PM CEST Moritz Fischer wrote:

Hi Alan, Federico,

On Fri, Aug 17, 2018 at 6:19 AM, Alan Tull [off-list ref] wrote:

quoted

On Fri, Aug 17, 2018, 2:00 AM Federico Vaga [off-list ref] 

wrote:

quoted

quoted

Hi Mortiz,

I'm not 100% into the problem to understand all cases. I'm putting on
the table the point of view, mainly, of an user. If you say there are
problems here or there I believe you. At the beginning, you did not
say that this interface may introduce problems (and I'm interested in
those problems since I
implemented one and we are using it), but that you fear that it
becomes
the
default (usually, being a default is a good thing).

Since you and Alan are working on this for a long time, you can read
each other mind, but I need a more verbose email to understand ^_^'

Of course the interface must be safe, I totally agree. In order to
make me understand what are the issues, can you list some of them?

Say you have kernel drivers (a network driver in the FPGA, or an I2C
controller) for example bound to hardware on a MMIO bus in the the FPGA.
You reprogram the FPGA using the debugfs interface, and the drivers don't
get unloaded correctly, the driver will try to access the registers and
depending on your system / bus either give you bad values or lock up.
Now userland locked up your system. Bad.

I think I got confused by your reference to the MMIO, but now it sound like 
it was just a very specific example of a more general problem. Because this 
is true for any device driver for FPGA soft-IP/IP-core, it is not strictly 
an MMIO problem. Am I missing something?

I get the problem, I have to fight with **this** problem daily because I'm 
loading images with:

cat hello.bin > /dev/fpga0

And then, somehow I have to load the device drivers (memory, IRQ, ...). But 
I will not say publicly what I do (it is a "don't try this at home" thing).

I'm not saying it isn't possible to do this if you're careful, of
course you could
first unload the drivers using rrmod and it would work just fine.

Or having some reference counter on the last loaded FPGA image may work. 
This way it will be possible to detect if there are users of the current 
FPGA and inhibit any unwanted FPGA load (like the module counter forbid 
rmmod when the device is in use). If a device driver is using some FPGA 
component the reference counter increase. How to do it? Need more studies, 
but probably this is a safe way that perhaps worth to look at.
 

I just feel an interface like this might make it easier to create the
wrong design.
I've seen plenty of Application notes from vendors where they literally
did "cat foo.bin > /dev/fpga" followed by mmap(/dev/mem...).

Actually, I'm doing worst than this (to compensate the lack of 
infrastructure). You tried, but you are not scaring me :P
 

quoted

Before we repeat what the doc l posted says, could you look at it and
comment on what I'm not saying there?

https://lkml.org/lkml/2018/8/15/525

Alan, maybe I didn't express myself well. I'm fine with the debugfs
interface as a debug interface, just not for general usage ;-) I think
your document is clear on that.

Thanks,

Moritz

-- 
Federico Vaga
[BE-CO-HT]