linux-kernel - Re: [RFC 0/5] Introduce NMI aware serial drivers

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Message-ID: <CAFA6WYPd-fcDkYNk1KrjYwD=FH3FBvjDGEoxCBBN9CRidoVXbw@mail.gmail.com>
Date:   Fri, 14 Aug 2020 17:36:36 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
        Jiri Slaby <jslaby@...e.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Jason Wessel <jason.wessel@...driver.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 0/5] Introduce NMI aware serial drivers

On Thu, 13 Aug 2020 at 15:47, Daniel Thompson
<daniel.thompson@...aro.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@...omium.org> wrote:
> > > On Wed, Aug 12, 2020 at 8:27 AM Doug Anderson <dianders@...omium.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.

-Sumit

>
> Daniel.