From: Stefan Christ <s.christ-guT5V/WYfQezQB+pC5nmwQ@public.gmane.org>
To: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
Cc: linux-watchdog-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 0/6] Implement I2C restart handler
Date: Wed, 6 Jul 2016 11:18:39 +0200 [thread overview]
Message-ID: <20160706091838.GC7031@lws-christ> (raw)
In-Reply-To: <20160705145839.GA3641@tetsubishi>
Hi,
On Tue, Jul 05, 2016 at 11:58:41PM +0900, Wolfram Sang wrote:
> Hi,
>
> > this is a request for feedback about a lockdep-warning-free I2C
> > restart_handler. I would like to know whether someone had the problem already
> > and how the best and mainline friendliest solution looks like.
> > I have an embedded board with the PMIC chip DA9063 that is also used as a
> > voltage regulator for DVFS. For a clean reboot/reset of the system I have to
> > set the bit nSHUTDOWN in the PMIC via I2C. The restart_handler call chain
> > is of type
> >
> > static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
> >
> > So any code running as a restart_handler cannot (should not) wait, for other
> > locks. When you use i2c_transfer/regmap you get lockdep warnings like [1].
>
> Yes, this problem has come up occasionally. And it is not only about
> sleeping. IRQs are disabled, too.
>
> My idea was to introduce master_xfer_irqless or similar to struct
> i2c_algorithm. I even discussed this shortly with Mark Brown how to
> interact with regmap; but this was too long ago, so I forgot what we
> agreed on :(
Great. I was looking for exactly this kind of feedback.
The term 'master_xfer_irqless' does not bring up anything on the internet and I
didn't find anything on the list linux-i2c. Can you point me to the discussion,
so I can read it up and work on it?
> > Any comments?
>
> I just skimmed very lightly over the patchset. Yet, seeing an I2C client
> messing directly with 'struct adapter' breaks so many abstractions, it
> hits my instant-NACK nerve ;)
Yes, accessing the function directly is really ugly. I was thinking about
augmenting the I2C interface and the regmap interface with 'sleep-free' and
'irq-less' functions or flags, but this requires changing a lot of code. So I
was just taking this shortcut. For follow up patches I will rework this.
Mit freundlichen Grüßen / Kind regards,
Stefan Christ
> Thanks,
>
> Wolfram
>
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next prev parent reply other threads:[~2016-07-06 9:18 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-05 13:22 [PATCH 0/6] Implement I2C restart handler Stefan Christ
2016-07-05 13:22 ` [RFC 1/6] watchdog: da9063_wdt: don't trigger watchdog too fast Stefan Christ
2016-07-05 15:33 ` Guenter Roeck
[not found] ` <577BD34F.7000804-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>
2016-07-06 8:42 ` Stefan Christ
2016-07-05 13:22 ` [RFC 2/6] watchdog: da9063_wdt: use delayed work to trigger Stefan Christ
2016-07-05 13:22 ` [RFC 3/6] i2c-imx: add blocking xfer function Stefan Christ
[not found] ` <1467724943-13416-1-git-send-email-s.christ-guT5V/WYfQezQB+pC5nmwQ@public.gmane.org>
2016-07-05 13:22 ` [RFC 4/6] i2c-core: add possibility to block an adapter for a single user Stefan Christ
2016-07-05 13:22 ` [RFC 6/6] watchdog: da9063_wdt: add schedule-free and race-free restart handler Stefan Christ
2016-07-05 15:37 ` Guenter Roeck
2016-07-05 13:22 ` [RFC 5/6] mfd: da9063: save i2c_client for later use Stefan Christ
2016-07-05 14:58 ` [PATCH 0/6] Implement I2C restart handler Wolfram Sang
2016-07-05 15:41 ` Guenter Roeck
2016-07-06 9:18 ` Stefan Christ [this message]
2016-07-06 14:16 ` Wolfram Sang
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