linux-kernel - Re: [PATCH v3 7/9] uio: add Xilinx user clock monitor support

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Message-ID: <2024082824-emphasis-thwarting-4ef4@gregkh>
Date: Wed, 28 Aug 2024 09:10:46 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Stephen Boyd <sboyd@...nel.org>
Cc: Harry Austen <hpausten@...tonmail.com>,
	Michael Turquette <mturquette@...libre.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Michal Simek <michal.simek@....com>,
	Shubhrajyoti Datta <shubhrajyoti.datta@....com>,
	Dave Ertman <david.m.ertman@...el.com>,
	Ira Weiny <ira.weiny@...el.com>, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 7/9] uio: add Xilinx user clock monitor support

On Tue, Aug 27, 2024 at 04:40:52PM -0700, Stephen Boyd wrote:
> Quoting Harry Austen (2024-08-27 12:08:52)
> > On Mon Aug 26, 2024 at 2:11 PM BST, Greg Kroah-Hartman wrote:
> > > On Mon, Aug 26, 2024 at 12:38:36PM +0000, Harry Austen wrote:
> > > > Xilinx clocking wizard IP core supports monitoring of up to four
> > > > optional user clock inputs, with a corresponding interrupt for
> > > > notification in change of clock state (stop, underrun, overrun or
> > > > glitch). Give userspace access to this monitor logic through use of the
> > > > UIO framework.
> > > >
> > > > Implemented as an auxiliary_driver to avoid introducing UIO dependency
> > > > to the main clock driver.
> > > >
> > > > Signed-off-by: Harry Austen <hpausten@...tonmail.com>
> > > > ---
> > > >  drivers/uio/Kconfig            |  8 ++++
> > > >  drivers/uio/Makefile           |  1 +
> > > >  drivers/uio/uio_xlnx_clk_mon.c | 71 ++++++++++++++++++++++++++++++++++
> > > >  3 files changed, 80 insertions(+)
> > > >  create mode 100644 drivers/uio/uio_xlnx_clk_mon.c
> > > >
> > > > diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
> > > > index b060dcd7c6350..ca8a53de26a67 100644
> > > > --- a/drivers/uio/Kconfig
> > > > +++ b/drivers/uio/Kconfig
> > > > @@ -164,4 +164,12 @@ config UIO_DFL
> > > >         opae-sdk/tools/libopaeuio/
> > > >
> > > >       If you compile this as a module, it will be called uio_dfl.
> > > > +
> > > > +config UIO_XLNX_CLK_MON
> > > > +   tristate "Xilinx user clock monitor support"
> > > > +   depends on COMMON_CLK_XLNX_CLKWZRD
> > > > +   help
> > > > +     Userspace I/O interface to the user clock monitor logic within the
> > > > +     Xilinx Clocking Wizard IP core.
> > >
> > > Why do you want a UIO api for a clock device?  What userspace code is
> > > going to access the hardware this way?  Why not use the normal
> > > kernel/user apis instead?
> > 
> > I was just trying to provide userspace access to these _unexpected_ clock
> > status event indications (clock stopped, underrun, overrun or glitched) and UIO

That is going to be a brand-new user/kernel api that isn't documented
anywhere and will be unique to this one device.  Please don't do that.

> Maybe unexpected events can be indicated through the EDAC subsystem,
> except that is usually about memory or cache errors, not device driver
> issues.

If you all need a new way to report issues like this to userspace, then
let's create the correct api for it, don't require userspace to mmap a
random device and expect to poke around in it safely to get the
information.

Odds are that mmap will change with the next version of this device,
right?

thanks,

greg k-h