Re: [RFC PATCH v3 2/2] pwm: imx: Configure output to GPIO in disabled state

[VokÃÄ Michal]

On 10.12.2018 12:17, Uwe Kleine-KÃnig wrote:
> On Mon, Dec 10, 2018 at 11:15:05AM +0000, VokÃÄ Michal wrote:
>> On 6.12.2018 17:16, Uwe Kleine-KÃnig wrote:
>>> On Thu, Dec 06, 2018 at 03:37:55PM +0000, VokÃÄ Michal wrote:
>>>> On 6.12.2018 14:59, Uwe Kleine-KÃnig wrote:
>>>>> On Thu, Dec 06, 2018 at 01:41:31PM +0000, VokÃÄ Michal wrote:
>>>>>
>>>>> Can it happen, that pinctrl_pins_pwm is PTR_ERR(-EPROBE_DEFER)?
>>>>
>>>> No. The pinctrl_lookup_state either returns pointer to the pinctrl state
>>>> or ERR_PTR(-ENODEV). But I do not explicitly test the pinctrl_pins_pwm
>>>> for PTR_ERR(-EPROBE_DEFER), or do I?
>>>
>>> You don't, I just wondered if this could happen and the function should
>>> return -EPROBE_DEFER in this case, too.
>>
>> OK.
>>
>>>>> Maybe you only want to ignore PTR_ERR(-ENODEV) and for example propagate
>>>>> -EIO? I think you want to put the gpio if the failure is because there
>>>>> is a pinctrl related error.
>>>>
>>>> I think that is what I am doing. In case the GPIO is not ready the probe
>>>> is deferred. In case of any other error with the GPIO or pinctrl failure
>>>> I put the pinctrl. Or maybe I do not really understand what you mean.
>>>
>>> Yes, you put the pinctrl, but not the GPIO. I.e. you're not undoing
>>> devm_gpiod_get_optional(). Maybe only do this if the pinctrl stuff
>>> succeeded to not touch the GPIO if it won't be used?
>>
>> OK, I agree it seems better to get the pinctrl first and if it succeeds
>> only then try to get the GPIO. In that case I need to use the non-optional
>> variant of devm_gpio_get(). Note that then I do not really need to put the
>> GPIO in the error path as it means I did not get it.
>> The code would look like:
>>
>> +static int imx_pwm_init_pinctrl_info(struct imx_chip *imx_chip,
>> +				      struct platform_device *pdev)
>> +{
>> +	imx_chip->pinctrl = devm_pinctrl_get(&pdev->dev);
>> +	if (IS_ERR(imx_chip->pinctrl)) {
>> +		dev_dbg(&pdev->dev, "can not get pinctrl\n");
>> +		return PTR_ERR(imx_chip->pinctrl);
>> +	}
>> +
>> +	imx_chip->pinctrl_pins_pwm = pinctrl_lookup_state(imx_chip->pinctrl,
>> +							  "pwm");
>> +	imx_chip->pinctrl_pins_gpio = pinctrl_lookup_state(imx_chip->pinctrl,
>> +							   "gpio");
>> +
>> +	if (IS_ERR(imx_chip->pinctrl_pins_pwm) ||
>> +	    IS_ERR(imx_chip->pinctrl_pins_gpio)) {
>> +		dev_dbg(&pdev->dev, "pinctrl information incomplete\n");
>> +		goto out;
>> +	}
>> +
>> +	imx_chip->pwm_gpiod = devm_gpiod_get(&pdev->dev, "pwm", GPIOD_IN);
>> +	if (PTR_ERR(imx_chip->pwm_gpiod) == -EPROBE_DEFER) {
>> +		return -EPROBE_DEFER;
>> +	} else if (IS_ERR(imx_chip->pwm_gpiod)) {
>> +		dev_dbg(&pdev->dev, "GPIO information incomplete\n");
>> +		goto out;
>> +	}
>> +
>> +	return 0;
>> +
>> +out:
>> +	devm_pinctrl_put(imx_chip->pinctrl);
>> +	imx_chip->pinctrl = NULL;
>> +
>> +	return 0;
>> +}
> 
> This looks right.

Wow, you're quick! OK, thanks.

>>>>> ISTR that there was a patch that implements get_state for imx. Is there
>>>>> a dependency on that one? Otherwise the state returned by
>>>>> pwm_get_state() might not be what is actually configured.
>>>>
>>>> No, it should be independent. One can go without the other. I tested all
>>>> three combinations (mainline with .get_state, mainline with this series,
>>>> mainline with .get_state AND this series) and got the expected results.
>>>> Without the .get_state() patch the core always returns the default which
>>>> is disabled state so the gpio pinctrl state is selected in probe.
>>>
>>> Without .get_state it won't be possible to smoothly take over a running
>>> PWM.
>>
>> But that is exactly how the current pwm-imx code works, right?
> 
> But then at least the pwm would run until the first consumer
> reconfigures it.

That is right. I think it is actually possible (and maybe good idea?)
to drop the probe part from this pinctrl/GPIO series and put it into
the .get_state series if the .get_state series would land in later.
What do you think?

Michal