From: Jerome Brunet <jbrunet@baylibre.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ulf Hansson <ulf.hansson@linaro.org>
Cc: Kevin Hilman <khilman@baylibre.com>,
"open list\:ARM\/Amlogic Meson..."
<linux-amlogic@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"linux-mmc\@vger.kernel.org" <linux-mmc@vger.kernel.org>,
Brad Harper <bjharper@gmail.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [PATCH] mmc: meson-gx: remove IRQF_ONESHOT
Date: Mon, 05 Oct 2020 14:31:06 +0200 [thread overview]
Message-ID: <1jlfgkrh11.fsf@starbuckisacylon.baylibre.com> (raw)
In-Reply-To: <87wo052grp.fsf@nanos.tec.linutronix.de>
On Mon 05 Oct 2020 at 10:55, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Mon, Oct 05 2020 at 10:22, Ulf Hansson wrote:
>> On Fri, 2 Oct 2020 at 18:49, Jerome Brunet <jbrunet@baylibre.com> wrote:
>>>
>>> IRQF_ONESHOT was added to this driver to make sure the irq was not enabled
>>> again until the thread part of the irq had finished doing its job.
>>>
>>> Doing so upsets RT because, under RT, the hardirq part of the irq handler
>>> is not migrated to a thread if the irq is claimed with IRQF_ONESHOT.
>>> In this case, it has been reported to eventually trigger a deadlock with
>>> the led subsystem.
>>>
>>> Preventing RT from doing this migration was certainly not the intent, the
>>> description of IRQF_ONESHOT does not really reflect this constraint:
>>>
>>> > IRQF_ONESHOT - Interrupt is not reenabled after the hardirq handler finished.
>>> > Used by threaded interrupts which need to keep the
>>> > irq line disabled until the threaded handler has been run.
>>>
>>> This is exactly what this driver was trying to acheive so I'm still a bit
>>> confused whether this is a driver or an RT issue.
>>>
>>> Anyway, this can be solved driver side by manually disabling the IRQs
>>> instead of the relying on the IRQF_ONESHOT. IRQF_ONESHOT may then be removed
>>> while still making sure the irq won't trigger until the threaded part of
>>> the handler is done.
>>
>> Thomas, may I have your opinion on this one.
>>
>> I have no problem to apply $subject patch, but as Jerome also
>> highlights above - this kind of makes me wonder if this is an RT
>> issue, that perhaps deserves to be solved in a generic way.
>>
>> What do you think?
>
> Let me stare at the core code. Something smells fishy.
FYI: initial discussion can be found here
https://lore.kernel.org/linux-amlogic/24a844c3-c2e0-c735-ccb7-83736218b548@gmail.com/
next prev parent reply other threads:[~2020-10-05 12:31 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 16:49 [PATCH] mmc: meson-gx: remove IRQF_ONESHOT Jerome Brunet
2020-10-05 8:22 ` Ulf Hansson
2020-10-05 8:55 ` Thomas Gleixner
2020-10-05 12:31 ` Jerome Brunet [this message]
2020-10-06 12:43 ` Thomas Gleixner
2020-10-06 13:45 ` Brad Harper
2020-10-06 15:33 ` Thomas Gleixner
2020-10-07 11:32 ` Jerome Brunet
2020-10-08 5:11 ` Brad Harper
2020-10-08 9:08 ` Ulf Hansson
2020-11-10 15:04 ` Jerome Brunet
2020-11-11 10:47 ` Ulf Hansson
2020-11-13 15:25 ` Jerome Brunet
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