From: Sumit Garg <sumit.garg@linaro.org>
To: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Doug Anderson <dianders@chromium.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-serial@vger.kernel.org,
kgdb-bugreport@lists.sourceforge.net,
Jiri Slaby <jslaby@suse.com>,
Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Jason Wessel <jason.wessel@windriver.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC 0/5] Introduce NMI aware serial drivers
Date: Mon, 17 Aug 2020 19:42:14 +0530 [thread overview]
Message-ID: <CAFA6WYOX0VzSvCyNTPemNMBPmSY75Q8vKdyQLc9cuq2m5eBWLg@mail.gmail.com> (raw)
In-Reply-To: <20200817092830.xcl2gkyxoe5grgnz@holly.lan>
On Mon, 17 Aug 2020 at 14:58, Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> On Mon, Aug 17, 2020 at 10:42:43AM +0530, Sumit Garg wrote:
> > On Fri, 14 Aug 2020 at 19:48, Daniel Thompson
> > <daniel.thompson@linaro.org> wrote:
> > >
> > > On Fri, Aug 14, 2020 at 05:36:36PM +0530, Sumit Garg wrote:
> > > > On Thu, 13 Aug 2020 at 15:47, Daniel Thompson
> > > > <daniel.thompson@linaro.org> wrote:
> > > > >
> > > > > On Thu, Aug 13, 2020 at 02:55:12PM +0530, Sumit Garg wrote:
> > > > > > On Thu, 13 Aug 2020 at 05:38, Doug Anderson <dianders@chromium.org> wrote:
> > > > > > > On Wed, Aug 12, 2020 at 8:27 AM Doug Anderson <dianders@chromium.org> wrote:
> > > > > > > > One
> > > > > > > > last worry is that I assume that most people testing (and even
> > > > > > > > automated testing labs) will either always enable NMI or won't enable
> > > > > > > > NMI. That means that everyone will be only testing one codepath or
> > > > > > > > the other and (given the complexity) the non-tested codepath will
> > > > > > > > break.
> > > > > > > >
> > > > > >
> > > > > > The current patch-set only makes this NMI to work when debugger (kgdb)
> > > > > > is enabled which I think is mostly suitable for development
> > > > > > environments. So most people testing will involve existing IRQ mode
> > > > > > only.
> > > > > >
> > > > > > However, it's very much possible to make NMI mode as default for a
> > > > > > particular serial driver if the underlying irqchip supports it but it
> > > > > > depends if we really see any production level usage of NMI debug
> > > > > > feature.
> > > > >
> > > > > The effect of this patch is not to make kgdb work from NMI it is to make
> > > > > (some) SysRqs work from NMI. I think that only allowing it to deploy for
> > > > > kgdb users is a mistake.
> > > > >
> > > > > Having it deploy automatically for kgdb users might be OK but it seems
> > > > > sensible to make this feature available for other users too.
> > > >
> > > > I think I wasn't clear enough in my prior reply. Actually I meant to
> > > > say that this patch-set enables NMI support for a particular serial
> > > > driver via ".poll_init()" interface and the only current user of that
> > > > interface is kgdb.
> > > >
> > > > So if there are other users interested in this feature, they can use
> > > > ".poll_init()" interface as well to enable it.
> > >
> > > Huh?
> > >
> > > We appear to speaking interchangably about users (people who sit in
> > > front of the machine and want a stack trace) and sub-systems ;-).
> > >
> > > I don't think other SysRq commands have quite such a direct relationship
> > > between the sub-system and the sysrq command. For example who are you
> > > expecting to call .poll_init() if a user wants to use the SysRq to
> > > provoke a stack trace?
> > >
> >
> > Ah, I see. So you meant to provide a user-space interface to
> > dynamically enable/disable NMI debug, correct? It will require IRQ <->
> > NMI switching at runtime which should be doable safely.
>
> I haven't given much thought to the exact mechanism, though I would
> perhaps have started by thinking about a module parameter).
>
> From an RFC point of view, I simple think this feature is potentially
> useful on systems without kgdb (which, let's be honest, are firmly in
> the majority) so making .poll_init() the only way to activate it is a
> mistake.
>
Makes sense, will add a module parameter to enable this feature during
boot as well.
-Sumit
>
> Daniel.
next prev parent reply other threads:[~2020-08-17 14:12 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 12:10 [RFC 0/5] Introduce NMI aware serial drivers Sumit Garg
2020-07-21 12:10 ` [RFC 1/5] tty/sysrq: Make sysrq handler NMI aware Sumit Garg
2020-08-12 23:59 ` Doug Anderson
2020-08-14 7:24 ` Sumit Garg
2020-08-14 14:34 ` peterz
2020-08-14 14:57 ` Doug Anderson
2020-08-17 14:08 ` Sumit Garg
2020-08-17 17:19 ` Doug Anderson
2020-08-18 13:30 ` Sumit Garg
2020-07-21 12:10 ` [RFC 2/5] serial: core: Add framework to allow NMI aware serial drivers Sumit Garg
2020-08-12 23:59 ` Doug Anderson
2020-08-13 14:19 ` Sumit Garg
2020-08-13 14:37 ` Doug Anderson
2020-08-14 11:17 ` Sumit Garg
2020-08-14 14:13 ` Daniel Thompson
2020-08-17 12:27 ` Sumit Garg
2020-08-17 13:57 ` Doug Anderson
2020-08-17 14:23 ` Sumit Garg
2020-08-17 14:32 ` Daniel Thompson
2020-08-18 13:18 ` Sumit Garg
2020-08-17 14:28 ` Daniel Thompson
2020-08-18 13:06 ` Sumit Garg
2020-08-14 14:43 ` Doug Anderson
2020-08-17 12:29 ` Sumit Garg
2020-07-21 12:10 ` [RFC 3/5] serial: amba-pl011: Re-order APIs definition Sumit Garg
2020-07-21 12:10 ` [RFC 4/5] serial: amba-pl011: Enable NMI aware uart port Sumit Garg
2020-08-12 23:59 ` Doug Anderson
2020-08-13 10:34 ` Sumit Garg
2020-07-21 12:10 ` [RFC 5/5] serial: Remove KGDB NMI serial driver Sumit Garg
2020-08-11 13:50 ` [RFC 0/5] Introduce NMI aware serial drivers Sumit Garg
2020-08-11 13:58 ` Greg Kroah-Hartman
2020-08-11 14:29 ` Sumit Garg
2020-08-11 14:58 ` Greg Kroah-Hartman
2020-08-11 17:15 ` Doug Anderson
2020-08-12 14:52 ` Sumit Garg
2020-08-12 15:27 ` Doug Anderson
2020-08-13 0:08 ` Doug Anderson
2020-08-13 9:25 ` Sumit Garg
2020-08-13 10:17 ` Daniel Thompson
2020-08-14 12:06 ` Sumit Garg
2020-08-14 14:18 ` Daniel Thompson
2020-08-17 5:12 ` Sumit Garg
2020-08-17 9:28 ` Daniel Thompson
2020-08-17 14:12 ` Sumit Garg [this message]
2020-08-13 15:26 ` Doug Anderson
2020-08-14 12:50 ` Sumit Garg
2020-08-12 5:48 ` Sumit Garg
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