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Date:   Tue, 23 Mar 2021 08:34:47 +0100
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Johan Hovold <johan@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sam Nobs <samuel.nobs@taitradio.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>, kernel@pengutronix.de
Subject: Re: [PATCH] serial: imx: drop workaround for forced irq threading
Message-ID: <20210323073447.r3utxintt5c3blb4@pengutronix.de>
References: <20210322111036.31966-1-johan@kernel.org>
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Hello Sebastian,

On Mon, Mar 22, 2021 at 09:48:36PM +0100, Sebastian Andrzej Siewior wrote:
> On 2021-03-22 14:40:32 [+0100], Uwe Kleine-K=C3=B6nig wrote:
> > From a strictly logically point of view you indeed cannot. But if you go
> > to the street and say to people there that they can park their car in
> > this street free of charge between Monday and Friday, I expect that most
> > of them will assume that they have to pay for parking on weekends.
>=20
> If I hear that parking is free on weekdays and on paid on weekends, I
> expect it to be a scam.

I don't feel taken seriously with this reply.

> Uwe, the patch reverts a change which was needed for !RT + threadirqs.

This would be a useful information for the commit log.

> The commit message claims that since the referenced commit "=E2=80=A6 int=
errupt
> handlers always run with interrupts disabled on non-RT=E2=80=A6 ". This h=
as
> nothing to do with _this_ change. It argues why the workaround is not
> needed.

It argues why the work around is not needed on non-RT. It might be
obvious for someone who is firm in the RT concepts, but IMHO commit logs
should be understandable by and make sense for a wider audience than the
deep experts. From what I know about RT "Force-threaded interrupt
handlers used to run with interrupts enabled" still applies there.

> If the referenced commit breaks RT then this is another story.

I'm surprised to hear that from you. With the goal to get RT into
mainline I would expect you to be happy if people consider the effects
on RT in their reviews.

> > So when you said that on on-RT the reason why it used to need a
> > workaround is gone made me wonder what that implies for RT.
>=20
> There was never reason (or a lockdep splat) for it on RT. If so you
> should have seen it, right?

No, I don't consider myself to be an RT expert who is aware of all the
problems. So I admit that for me the effect on RT of the patch under
discussion isn't obvious. I just wonder that the change is justified
with being OK on non-RT. So it's either bad that it breaks RT *or*
improving the commit log would be great.

And even if I had reason to believe that there is no problem with the
commit on RT, I'd still wish that the commit log wouldn't suggest to the
casual reader that there might be a problem.

Best regards
Uwe

--=20
Pengutronix e.K.                           | Uwe Kleine-K=C3=B6nig         =
   |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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