Messages in this thread | | | Date | Mon, 6 Mar 2023 12:21:44 +0100 | From | Mike Looijmans <> | Subject | Re: [PATCH v3 2/2] iio: adc: Add TI ADS1100 and ADS1000 |
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Met vriendelijke groet / kind regards,
Mike Looijmans System Expert
TOPIC Embedded Products B.V. Materiaalweg 4, 5681 RJ Best The Netherlands
T: +31 (0) 499 33 69 69 E: mike.looijmans@topicproducts.com W: www.topic.nl
Please consider the environment before printing this e-mail On 04-03-2023 18:57, Jonathan Cameron wrote: > On Tue, 28 Feb 2023 07:31:51 +0100 > Mike Looijmans <mike.looijmans@topic.nl> wrote: > >> The ADS1100 is a 16-bit ADC (at 8 samples per second). >> The ADS1000 is similar, but has a fixed data rate. >> >> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl> > Hi Mike, > > A few minor things + one request for a test as trying to chase a possible > ref count overflow around the runtime_pm was giving me a enough of a headache > that it's easier to ask you just to poke it and see. If it doesn't fail as > I expect I'll take a closer look! > > Jonathan > > ... >> + data->client = client; >> + mutex_init(&data->lock); >> + >> + indio_dev->name = "ads1100"; >> + indio_dev->modes = INDIO_DIRECT_MODE; >> + indio_dev->channels = &ads1100_channel; >> + indio_dev->num_channels = 1; >> + indio_dev->info = &ads1100_info; >> + >> + data->reg_vdd = devm_regulator_get(dev, "vdd"); >> + if (IS_ERR(data->reg_vdd)) >> + return dev_err_probe(dev, PTR_ERR(data->reg_vdd), >> + "Failed to get vdd regulator\n"); >> + >> + ret = regulator_enable(data->reg_vdd); >> + if (ret < 0) >> + return dev_err_probe(dev, PTR_ERR(data->reg_vdd), >> + "Failed to enable vdd regulator\n"); >> + >> + ret = devm_add_action_or_reset(dev, ads1100_reg_disable, data->reg_vdd); >> + if (ret) >> + return ret; > Please could you check a subtle interaction of runtime pm and this devm managed > flow. > > I think we can hit the following flow. > 1) In runtime suspend (wait long enough for this to happen). > 2) Unbind the driver (rmmod will do) > 3) During the unbind we exit suspend then enter it again before we call remove > (that's just part of the normal remove flow). > 4) We then end up calling regulator disable when it's already disabled. > > We've traditionally avoided that by having the remove explicitly call > pm_runtime_get_sync() before we then disable runtime pm. I don't > think that happens with devm_pm_runtime_enable() but I could be missing > a path where it does. > > If the sequence goes wrong you should get a warning about an unbalanced regulator > disable. The fix would be an extra devm_add_action_or_reset() before the > devm_iio_device_register() below that just calls pm_runtime_get_sync() > to force the state to on. > > Gah. These subtle paths always give me a headache. > We don't normally have too much problem with this because many > runtime_resume / suspend functions don't change reference counts.
Just did this test, waited a few seconds, checked /sys/kernel/debug/regulator... that the regulator had been disabled.
Then executed: echo -n 3-004a > /sys/bus/i2c/drivers/ads1100/unbind
to unload the driver, and no messages were added to the kernel log.
I could see the driver going away and removing itself from iio and regulators.
Tried this a couple of times (using bind/unbind), and no problem reported.
Hopes this helps with your headaches...
-- Mike Looijmans
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