On 06/04/16 15:58, Laxman Dewangan wrote:
> Hi Daniel,
>
>
> On Wednesday 06 April 2016 07:19 PM, Daniel Baluta wrote:
>> On Wed, Apr 6, 2016 at 1:31 PM, Laxman Dewangan <ldewangan@xxxxxxxxxx> wrote:
>>> Some of kernel driver uses the IIO framework to get the sensor
>>> value via ADC or IIO HW driver. The client driver get iio channel
>>> by iio_channel_get() and release it by calling iio_channel_release().
>>>
>>> Add resource managed version (devm_*) of these APIs so that if client
>>> calls the devm_iio_channel_get() then it need not to release it explicitly,
>>> it can be done by managed device framework when driver get un-binded.
>>>
>>> This reduces the code in error path and also need of .remove callback in
>>> some cases.
>>>
>> Please provide at least one example of code that uses this API.
>
> Most of client for this APIs are in other subsystem.
> When I was working on the patch
> [PATCH 2/2] thermal: generic-adc: Add ADC based thermal sensor driver
>
> if I have devm_iio_channel_get() then I can get .remove callback at all.
>
> I did not use this new APIs in my patch because they are in different subsystem.
It's actually worse than that having taken a quick look at the generic-adc thermal patch
you reference above.
(perhaps worth cc'ing linux-iio for next version of that).
Without this devm function set you have a race in remove in which I think you can
get attempts to access the channels after they have been released...
> +
> + gti->tz_dev = devm_thermal_zone_of_sensor_register(&pdev->dev, 0,
> + gti, &gadc_thermal_ops);
> + if (IS_ERR(gti->tz_dev)) {
> + ret = PTR_ERR(gti->tz_dev);
> + dev_err(&pdev->dev, "Thermal zone sensor register failed: %d\n",
> + ret);
> + goto sensor_fail;
> + }
This will get cleaned up in remove 'after' the iio_channels are released.
Hence you have a race in which they can probably be accessed after release
(unless some magic is going on that I've missed).
> +
> + return 0;
> +
> +sensor_fail:
> + iio_channel_release(gti->channel);
> + return ret;
> +}
> +
> +static int gadc_thermal_remove(struct platform_device *pdev)
> +{
> + struct gadc_thermal_info *gti = platform_get_drvdata(pdev);
> +
> + iio_channel_release(gti->channel);
> +
> + return 0;
> +}
> +
>
>
>
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