linux-kernel - Re: [PATCH V7 6/6] backlight: qcom-wled: Add auto string detection logic

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Message-ID: <20191017133024.GQ4365@dell>
Date:   Thu, 17 Oct 2019 14:30:24 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     kgunda@...eaurora.org
Cc:     bjorn.andersson@...aro.org, jingoohan1@...il.com,
        b.zolnierkie@...sung.com, dri-devel@...ts.freedesktop.org,
        daniel.thompson@...aro.org, jacek.anaszewski@...il.com,
        pavel@....cz, robh+dt@...nel.org, mark.rutland@....com,
        linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH V7 6/6] backlight: qcom-wled: Add auto string detection
 logic

On Thu, 17 Oct 2019, kgunda@...eaurora.org wrote:

> On 2019-10-17 17:56, Lee Jones wrote:
> > On Wed, 16 Oct 2019, Kiran Gunda wrote:
> > 
> > > The auto string detection algorithm checks if the current WLED
> > > sink configuration is valid. It tries enabling every sink and
> > > checks if the OVP fault is observed. Based on this information
> > > it detects and enables the valid sink configuration.
> > > Auto calibration will be triggered when the OVP fault interrupts
> > > are seen frequently thereby it tries to fix the sink configuration.
> > > 
> > > The auto-detection also kicks in when the connected LED string
> > > of the display-backlight malfunctions (because of damage) and
> > > requires the damaged string to be turned off to prevent the
> > > complete panel and/or board from being damaged.
> > > 
> > > Signed-off-by: Kiran Gunda <kgunda@...eaurora.org>
> > > ---
> > >  drivers/video/backlight/qcom-wled.c | 410
> > > +++++++++++++++++++++++++++++++++++-
> > >  1 file changed, 404 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/video/backlight/qcom-wled.c
> > > b/drivers/video/backlight/qcom-wled.c
> > > index b5b125c..ff7c409 100644
> > > --- a/drivers/video/backlight/qcom-wled.c
> > > +++ b/drivers/video/backlight/qcom-wled.c

[...]

> > > +		if (int_sts & WLED3_CTRL_REG_OVP_FAULT_STATUS)
> > > +			dev_dbg(wled->dev, "WLED OVP fault detected with SINK %d\n",
> > > +				i + 1);
> > 
> > I haven't reviewed the whole patch, but this caught my eye.
> > 
> > I think this should be upgraded to dev_warn().
> > 
> Thought of keeping these messages silent, Because the string configuration
> will be corrected in this
> and informing it at end of the auto string detection.

[...]

> > > +	} else {
> > > +		dev_warn(wled->dev, "New WLED string configuration found %x\n",
> > > +			 sink_valid);
> > 
> > Why would the user care about this?  Is it not normal?
> > 
> Actually, it comes here if the user provided string configuration in the
> device tree is in-correct.
> That's why just informing the user about the right string configuration,
> after the auto string detection.

Then I think we need to be more forthcoming.  Tell the user the
configuration is incorrect and what you've done to rectify it.

"XXX is not a valid configuration - using YYY instead"

[...]

> > > +static int wled_configure_ovp_irq(struct wled *wled,
> > > +				  struct platform_device *pdev)
> > > +{
> > > +	int rc;
> > > +	u32 val;
> > > +
> > > +	wled->ovp_irq = platform_get_irq_byname(pdev, "ovp");
> > > +	if (wled->ovp_irq < 0) {
> > > +		dev_dbg(&pdev->dev, "ovp irq is not used\n");
> > 
> > I assume this is optional.  What happens if no IRQ is provided?
> > 
> Here OVP IRQ is used to detect the wrong string detection. If it is not
> provided the auto string detection logic won't work.

"OVP IRQ not found - disabling automatic string detection"

> > If, for instance, polling mode is enabled, maybe something like this
> > would be better?
> > 
> >       dev_warn(&pdev->dev, "No IRQ found, falling back to polling
> > mode\n");

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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