Re: [PATCH v3 1/5] fpga: dfl: rename the bus type "dfl" to "fpga-dfl"

[Xu Yilun]

On Mon, Sep 28, 2020 at 09:19:00PM -0700, Moritz Fischer wrote:
> Hi Xu,
> 
> On Tue, Sep 29, 2020 at 09:23:23AM +0800, Xu Yilun wrote:
> > Hi moritz:
> > 
> > On Sun, Sep 27, 2020 at 04:36:47PM +0800, Xu Yilun wrote:
> > > Hi Greg,
> > > 
> > > On Sun, Sep 27, 2020 at 09:54:01AM +0200, Greg KH wrote:
> > > > On Sun, Sep 27, 2020 at 03:37:54PM +0800, Xu Yilun wrote:
> > > > > Hi Greg,
> > > > > 
> > > > > On Sun, Sep 27, 2020 at 07:51:08AM +0200, Greg KH wrote:
> > > > > > On Sat, Sep 26, 2020 at 12:22:19PM -0700, Moritz Fischer wrote:
> > > > > > > Hi Greg,
> > > > > > > 
> > > > > > > On Sat, Sep 26, 2020 at 08:09:13AM +0200, Greg KH wrote:
> > > > > > > > On Sat, Sep 26, 2020 at 10:23:46AM +0800, Xu Yilun wrote:
> > > > > > > > > Hi greg,
> > > > > > > > > 
> > > > > > > > > About the bus naming, I summarized some questions we've discussed to check
> > > > > > > > > with you. See inline.
> > > > > > > > > 
> > > > > > > > > On Thu, Sep 24, 2020 at 10:27:00AM -0700, Moritz Fischer wrote:
> > > > > > > > > > Hi Xu,
> > > > > > > > > > 
> > > > > > > > > > On Fri, Sep 25, 2020 at 12:59:57AM +0800, Xu Yilun wrote:
> > > > > > > > > > > Now the DFL device drivers could be made as independent modules and put
> > > > > > > > > > > in different subsystems according to their functionalities. So the name
> > > > > > > > > > > should be descriptive and unique in the whole kernel.
> > > > > > > > > > > 
> > > > > > > > > > > The patch changes the naming of dfl bus related structures, functions,
> > > > > > > > > > > APIs and documentations.
> > > > > > > > > > > 
> > > > > > > > > > > Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxx>
> > > > > > > > > > > ---
> > > > > > > > > > >  Documentation/ABI/testing/sysfs-bus-dfl      |  15 --
> > > > > > > > > > >  Documentation/ABI/testing/sysfs-bus-fpga-dfl |  15 ++
> > > > > > > > > > >  MAINTAINERS                                  |   2 +-
> > > > > > > > > > >  drivers/fpga/dfl.c                           | 254 ++++++++++++++-------------
> > > > > > > > > > >  drivers/fpga/dfl.h                           |  77 ++++----
> > > > > > > > > > >  5 files changed, 184 insertions(+), 179 deletions(-)
> > > > > > > > > > >  delete mode 100644 Documentation/ABI/testing/sysfs-bus-dfl
> > > > > > > > > > >  create mode 100644 Documentation/ABI/testing/sysfs-bus-fpga-dfl
> > > > > > > > > > > 
> > > > > > > > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-dfl b/Documentation/ABI/testing/sysfs-bus-dfl
> > > > > > > > > > > deleted file mode 100644
> > > > > > > > > > > index 23543be..0000000
> > > > > > > > > > > --- a/Documentation/ABI/testing/sysfs-bus-dfl
> > > > > > > > > > > +++ /dev/null
> > > > > > > > > > > @@ -1,15 +0,0 @@
> > > > > > > > > > > -What:		/sys/bus/dfl/devices/dfl_dev.X/type
> > > > > > > > > > > -Date:		Aug 2020
> > > > > > > > > > > -KernelVersion:	5.10
> > > > > > > > > > > -Contact:	Xu Yilun <yilun.xu@xxxxxxxxx>
> > > > > > > > > > > -Description:	Read-only. It returns type of DFL FIU of the device. Now DFL
> > > > > > > > > > > -		supports 2 FIU types, 0 for FME, 1 for PORT.
> > > > > > > > > > > -		Format: 0x%x
> > > > > > > > > > > -
> > > > > > > > > > > -What:		/sys/bus/dfl/devices/dfl_dev.X/feature_id
> > > > > > > > > > > -Date:		Aug 2020
> > > > > > > > > > > -KernelVersion:	5.10
> > > > > > > > > > > -Contact:	Xu Yilun <yilun.xu@xxxxxxxxx>
> > > > > > > > > > > -Description:	Read-only. It returns feature identifier local to its DFL FIU
> > > > > > > > > > > -		type.
> > > > > > > > > > > -		Format: 0x%x
> > > > > > > > > > 
> > > > > > > > > > You're changing userland facing ABI. I think that's something to avoid,
> > > > > > > > > > please check with Greg on the rules since this hasn't been in a release yet.
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > I'm going to change the name of bus stuff for other subsystems, to be
> > > > > > > > > aligned, I also consider change the bus_type.name and dfl dev_name. But
> > > > > > > > > it will cause the changing of user ABIs. No user case for these user ABI
> > > > > > > > > now cause they are just queued, is it good I change them?
> > > > > > > > 
> > > > > > > > Why change the user name here?  No need for that, right?  Unless you
> > > > > > > > really want to, and think that no one will notice.  If so, fine, change
> > > > > > > > them :)
> > > > > > > 
> > > > > > > Let's leave it as is -- An FPGA is one possible implementation and as for
> > > > > > > other buses, you wouldn't call it fpga-usb or usb-fpga just because the
> > > > > > > USB bus is implemented in an FPGA if it behaves like a normal USB bus.
> > > > > > > Having an ASIC based DFL bus show up under dfl-fpga / fpga-dfl in sysfs
> > > > > > > would be super confusing.
> > > 
> > > I thought we have consensus that "dfl" could be used out of fpga domain.
> > > And we are all good that we keep the user ABIs & the bus name - "dfl", so "dfl"
> > > is good as a global name from linux user's point of view, is it?
> > > 
> > > But why we reject the "dfl" in kernel code domain? I thought it is very
> > > similar situation.
> > > 
> > > 
> > > I think we have 2 options, to make the dfl self-consistent:
> > > 
> > > 1. "dfl-fpga" for everything - bus name, user ABIs, structures & APIs for
> > >    other kernel subsystems. Then we lose the chance to support ASIC based DFL,
> > >    it would be hard if we change user ABIs later.
> > > 
> > > 2. "dfl" for everything.
> > > 
> > > BTW, no ASIC based DFL devices in kernel today.
> > > 
> > > I fully understand the word "naming is hard" now, help me :)
> > 
> > Seems now we have different opinions on this:
> > 
> > - Hao thinks self-consistent is important to dfl framework.
> Agreed. I mostly care about userspace facing ABI, though.
> 
> > - "dfl" for everything seems not preferable to Greg.
> Maybe now that we re-explained, we can take another look at that?

Seems "dfl" for everything is the one, agreed by Moritz, Hao and Yilun.

I'll wait for some time, to see if Greg could comment on it.

Thanks,
Yilun

> 
> > - From your previous mail, I assume you prefer to keep the bus name as "dfl"
> > but change the stuff for other subsystem, is it?
> 
> I mostly think we should keep DFL generic where it touches userspace and
> defines ABI, since we cannot change it afterwards.
> 
> I rest my point with the bus being independent of FPGAs despite the FPGA
> being the (currently) only user.
> 
> > So I got a little stuck here.
> > 
> > Do you think "dfl-fpga" for everything would be an acceptable solution
> > for you?
> 
> I just think it doesn't make a lot of sense to call it fpga-dfl or
> dfl-fpga. But if everyone else disagrees ... naming is hard :-)
> 
> Cheers,
> Moritz