Re: [PATCH v2] backlight: pwm: reject legacy pwm request for device defined in dt

[Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>]

Hi Boris,

On 12.10.2015 16:30, Boris Brezillon wrote:
> Hi Vladimir,
> 
> On Mon, 12 Oct 2015 15:16:44 +0200
> Nicolas Ferre <nicolas.ferre@atmel.com> wrote:
> 
>> Le 12/10/2015 14:29, Vladimir Zapolskiy a écrit :
>>> Platform PWM backlight data provided by board's device tree should be
>>> complete enough to successfully request a pwm device using pwm_get()
>>> API. This change fixes a bug, when an arbitrary (first found) PWM is
>>> connected to a "pwm-backlight" compatible device, when explicit PWM
>>> device reference is not given.
>>>
>>> Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
>>> already describes "pwms" as a required property, instead of blind
>>> selection of a potentially wrong PWM reject legacy PWM device
>>> registration request, leave legacy API only for non-dt cases.
>>>
>>> Based on initial implementation done by Dmitry Eremin-Solenikov.
>>>
>>> Reported-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
>>> Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
>>> Acked-by: Thierry Reding <thierry.reding@gmail.com>
>>> Acked-by: Lee Jones <lee.jones@linaro.org>
>>
>> It seems good to me:
>> Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
>>
>> (Adding some people to the Cc: list).
>>
>>
>>> ---
>>> The change is based on lee-backlight/for-backlight-next
>>>
>>> Changes from v1 to v2:
>>> * rebased on top of Nicolas' commit
>>>     68feaca0b13 ("backlight: pwm: Handle EPROBE_DEFER while requesting the PWM")
>>>
>>> Links to previous discussions of the change:
>>> * https://patchwork.ozlabs.org/patch/483993/
>>> * https://patchwork.ozlabs.org/patch/398849/
>>>
>>>  drivers/video/backlight/pwm_bl.c | 19 +++++++++----------
>>>  1 file changed, 9 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
>>> index eff379b..ae3c6b6 100644
>>> --- a/drivers/video/backlight/pwm_bl.c
>>> +++ b/drivers/video/backlight/pwm_bl.c
>>> @@ -271,19 +271,18 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>>>  	}
>>>  
>>>  	pb->pwm = devm_pwm_get(&pdev->dev, NULL);
>>> -	if (IS_ERR(pb->pwm)) {
>>> -		ret = PTR_ERR(pb->pwm);
>>> -		if (ret = -EPROBE_DEFER)
>>> -			goto err_alloc;
>>> -
>>> +	if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER
>>> +	    && !pdev->dev.of_node) {
>>>  		dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
>>>  		pb->legacy = true;
>>>  		pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
>>> -		if (IS_ERR(pb->pwm)) {
>>> -			dev_err(&pdev->dev, "unable to request legacy PWM\n");
>>> -			ret = PTR_ERR(pb->pwm);
>>> -			goto err_alloc;
>>> -		}
>>> +	}
>>> +
>>> +	if (IS_ERR(pb->pwm)) {
>>> +		ret = PTR_ERR(pb->pwm);
>>> +		if (ret != -EPROBE_DEFER)
>>> +			dev_err(&pdev->dev, "unable to request PWM\n");
>>> +		goto err_alloc;
>>>  	}
>>>  
>>>  	dev_dbg(&pdev->dev, "got pwm for backlight\n");
>>>
>>
>>
> 
> I still think it would be cleaner to do what Thierry proposed here [1].
> IMO, embedding the complexity of different error cases depending on the
> way PWM devices were defined (OF, pdata, ...) is rather risky and
> make the code even more complicated.

please correct me if I'm wrong, I suppose Thierry's change fixes
Nicolas' commit 68feaca0b13 only, and the intention of my change is to
fix an absolutely unrelated problem, see the commit message.

So, since still there is a remained chance of getting -EPROBE_DEFER from
pwm_get(), e.g. from of_pwm_get() or failed pwmchip_find_by_name() or
pwm->chip->ops->request() I don't see how Thierry's change alone may
help me to overcome the problem I'm trying to solve here.

> Best Regards,
> 
> Boris
> 
> [1]https://lkml.org/lkml/2015/10/5/319
> 
> 

--
With best wishes,
Vladimir