linux-kernel - Re: [PATCH v12 0/2] UIO support for dfl devices

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Date:   Wed, 24 Mar 2021 14:17:08 -0700
From:   Moritz Fischer <mdf@...nel.org>
To:     Xu Yilun <yilun.xu@...el.com>
Cc:     mdf@...nel.org, gregkh@...uxfoundation.org,
        linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org,
        trix@...hat.com, lgoncalv@...hat.com, hao.wu@...el.com
Subject: Re: [PATCH v12 0/2] UIO support for dfl devices

Hi Xu,

On Wed, Mar 24, 2021 at 04:22:17PM +0800, Xu Yilun wrote:
> Hi Moritz:
> 
> Sorry I need to get back to you again, seems no more comments from Greg.
> 
> The patchset is stuck here for more than 1 month. Do you have some
> more suggestion that could make it move forward? Do you have some more
> comments? Or give an acked-by? Or could you apply it to your fpga branch
> and go with next pull request?

In its current form it's a UIO driver and needs at least Greg's Acked-by
before I could apply it.

Greg, can you take another look?

> 
> Thanks,
> Yilun
> 
> On Mon, Mar 08, 2021 at 09:59:34AM +0800, Xu Yilun wrote:
> > This patchset supports some dfl device drivers written in userspace.
> > 
> > There are some Q&A about why UIO driver is needed in v11:
> > 
> > >From Greg:
> >   Why are you saying that an ethernet driver should be using the UIO
> >   interface?
> > 
> >   And why can't you use the existing UIO drivers that bind to memory
> >   regions specified by firmware?  Without an interrupt being used, why is
> >   UIO needed at all?
> > 
> > >From Moritz:
> >   Essentially I see two options:
> >   - Have a DFL bus driver instantiate a platform driver (uio_pdrv_genirq)
> >     which I *think* you described above?
> >   - What this patch implements -- a UIO driver on the DFL bus
> > 
> >   These FPGA devices can on the fly change their contents and -- even if
> >   just for test -- being able to expose a bunch of registers via UIO can
> >   be extremely useful.
> > 
> >   Whether a device should expose registers or not should be up to the
> >   implemeneter of the FPGA design I think (policy). This patch (or the
> >   previous version) provides a mechanism to do so via DFL.
> > 
> >   This is similar in nature to uio_pdrv_genirq on a DT based platform, to
> >   expose the registers you instantiate the DT node.
> > 
> >   Re-implementing a new driver for each of these instances doesn't seem
> >   desirable and tying DFL as enumeration mechanism to UIO seems like a
> >   good compromise for enabling this kind of functionality.
> > 
> >   Note this is *not* an attempt to bypass the network stack or other
> >   existing subsystems.
> > 
> > See the original message in:
> >   https://lore.kernel.org/linux-fpga/YDvQ8aO8v3NhLKzx@epycbox.lan/T/#m66ba2c96848e3dea38d1a4f16dfea3cb291f7975
> > 
> > 
> > >From Yilun:
> >   The ETH GROUP IP is not designed as the full functional ethernet
> >   controller. It is specially developed for the Intel N3000 NIC. Since it
> >   is an FPGA based card, it is designed for the users to runtime reload
> >   part of the MAC layer logic developed by themselves, while the ETH GROUP
> >   is another part of the MAC which is not expected to be reloaded by
> >   customers, but it provides some configurations for software to work with
> >   the user logic.
> > 
> >   So I category the feature as the devices that "designed for specific
> >   purposes and does not fit into one of the standard kernel subsystems".
> >   Some related description could be found in Patch #2, to illustrate why
> >   using UIO for some DFL devices.
> > 
> >   There are now UIO drivers for PCI or platform devices, but in this case
> >   we are going to export a DFL(Device Feature List) bus device to
> >   userspace, a DFL driver for UIO is needed to bind to it.
> > 
> > See the original message in:
> >   https://lore.kernel.org/linux-fpga/YDvQ8aO8v3NhLKzx@epycbox.lan/T/#m91b303fd61485644353fad1e1e9c11d528844684
> > 
> > 
> > Xu Yilun (2):
> >   uio: uio_dfl: add userspace i/o driver for DFL bus
> >   Documentation: fpga: dfl: Add description for DFL UIO support
> > 
> >  Documentation/fpga/dfl.rst | 26 ++++++++++++++++++
> >  MAINTAINERS                |  1 +
> >  drivers/uio/Kconfig        | 17 ++++++++++++
> >  drivers/uio/Makefile       |  1 +
> >  drivers/uio/uio_dfl.c      | 66 ++++++++++++++++++++++++++++++++++++++++++++++
> >  5 files changed, 111 insertions(+)
> >  create mode 100644 drivers/uio/uio_dfl.c
> > 
> > -- 
> > 2.7.4

Thanks,
Moritz