From: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>
To: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>,
Stefan Christ <s.christ-guT5V/WYfQezQB+pC5nmwQ@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: Tue, 5 Jul 2016 08:41:04 -0700 [thread overview]
Message-ID: <577BD510.1070506@roeck-us.net> (raw)
In-Reply-To: <20160705145839.GA3641@tetsubishi>
On 07/05/2016 07:58 AM, 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 :(
>
>> 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 ;)
>
My NACK would be for two other reasons: First, for bypassing the watchdog core
for handling the minimum time between heartbeats, second for bypassing
the watchdog core to implement a reboot handler. Both are inadequately
or not at all explained.
Guenter
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WARNING: multiple messages have this Message-ID (diff)
From: Guenter Roeck <linux@roeck-us.net>
To: Wolfram Sang <wsa@the-dreams.de>, Stefan Christ <s.christ@phytec.de>
Cc: linux-watchdog@vger.kernel.org, linux-i2c@vger.kernel.org
Subject: Re: [PATCH 0/6] Implement I2C restart handler
Date: Tue, 5 Jul 2016 08:41:04 -0700 [thread overview]
Message-ID: <577BD510.1070506@roeck-us.net> (raw)
In-Reply-To: <20160705145839.GA3641@tetsubishi>
On 07/05/2016 07:58 AM, 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 :(
>
>> 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 ;)
>
My NACK would be for two other reasons: First, for bypassing the watchdog core
for handling the minimum time between heartbeats, second for bypassing
the watchdog core to implement a reboot handler. Both are inadequately
or not at all explained.
Guenter
next prev parent reply other threads:[~2016-07-05 15:41 UTC|newest]
Thread overview: 21+ 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 ` 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
2016-07-06 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 ` 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 13:22 ` 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 [this message]
2016-07-05 15:41 ` Guenter Roeck
2016-07-06 9:18 ` Stefan Christ
2016-07-06 9:18 ` Stefan Christ
2016-07-06 14:16 ` Wolfram Sang
2016-07-06 14:16 ` Wolfram Sang
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