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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