linux-kernel - Re: [PATCH V1 4/5] backlight: qcom-wled: Add support for OVP interrupt handling

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Date:   Wed, 09 May 2018 11:46:30 +0530
From:   kgunda@...eaurora.org
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-leds@...r.kernel.org, linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH V1 4/5] backlight: qcom-wled: Add support for OVP
 interrupt handling

On 2018-05-09 10:36, kgunda@...eaurora.org wrote:
> On 2018-05-08 22:49, Bjorn Andersson wrote:
>> On Tue 08 May 05:26 PDT 2018, kgunda@...eaurora.org wrote:
>> 
>>> On 2018-05-07 22:51, Bjorn Andersson wrote:
>>> > On Thu 03 May 02:57 PDT 2018, Kiran Gunda wrote:
>> [..]
>>> > > @@ -220,7 +255,12 @@ static int wled_module_enable(struct wled
>>> > > *wled, int val)
>>> > >  				WLED3_CTRL_REG_MOD_EN,
>>> > >  				WLED3_CTRL_REG_MOD_EN_MASK,
>>> > >  				WLED3_CTRL_REG_MOD_EN_MASK);
>>> > > -	return rc;
>>> > > +	if (rc < 0)
>>> > > +		return rc;
>>> > > +
>>> > > +	schedule_delayed_work(&wled->ovp_work, WLED_SOFT_START_DLY_US);
>>> >
>>> > Do you really want to delay the work on disable?
>>> >
>>> > Wouldn't it be better to use a delay worker for the enablement and in
>>> > the disable case you cancel the work and just disable_irq() directly
>>> > here.
>>> >
>>> Sure. Will do it in the next series.
>>> > But more importantly, if this is only related to auto detection, do you
>>> > really want to enable/disable the ovp_irq after you have detected the
>>> > string configuration?
>>> >
>>> Ok. This is used for the genuine OVP detection and for the auto 
>>> detection as
>>> well.
>> 
>> What is the expected outcome of detecting an OVP condition, outside 
>> auto
>> detection?
>> 
> Ok... Out side auto detection, it is used for information purpose. I 
> think it is
> okay to ignore enable/disable the ovp_irq after auto detection is done.

I am taking back the above comment. The OVP irq is needed even after the 
auto detection is done.
Because there are also cases where one/more of the connected LED string 
of the display-backlight
is malfunctioning (due to damage) and requires the damaged string to be 
turned off to prevent the
complete panel and/or board from being damaged by running the auto 
detection again.

currently we are not resetting "auto_detection_done" flag once it set to 
true. I will fix it in
the next series to run the auto detection again (If the OVP condition is 
met) because of the
above mentioned reason.

We are going to discuss the HW systems to check if the OVP keep on 
occurring due to some other
reason, other then the string issue, what needs to do (disable the 
module ?).

>> Regards,
>> Bjorn
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