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

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Date:   Thu, 17 Oct 2019 14:39:54 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     kgunda@...eaurora.org
Cc:     bjorn.andersson@...aro.org, jingoohan1@...il.com,
        lee.jones@...aro.org, b.zolnierkie@...sung.com,
        dri-devel@...ts.freedesktop.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, Oct 17, 2019 at 05:47:47PM +0530, kgunda@...eaurora.org wrote:
> On 2019-10-17 16:59, Daniel Thompson wrote:
> > On Wed, Oct 16, 2019 at 03:43:46PM +0530, 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>
> > 
> > It's a complex bit of code but I'm OK with it in principle. Everything
> > below is about small details and/or nitpicking.
> > 
> > 
> > > +static void wled_ovp_work(struct work_struct *work)
> > > +{
> > > +	struct wled *wled = container_of(work,
> > > +					 struct wled, ovp_work.work);
> > > +	enable_irq(wled->ovp_irq);
> > > +}
> > > +
> > 
> > A bit of commenting about why we have to wait 10ms before enabling the
> > OVP interrupt would be appreciated.
> > 
> > 
> Sure. Will add the comment in the next series.
> > > +static irqreturn_t wled_ovp_irq_handler(int irq, void *_wled)
> > > +{
> > > +	struct wled *wled = _wled;
> > > +	int rc;
> > > +	u32 int_sts, fault_sts;
> > > +
> > > +	rc = regmap_read(wled->regmap,
> > > +			 wled->ctrl_addr + WLED3_CTRL_REG_INT_RT_STS, &int_sts);
> > > +	if (rc < 0) {
> > > +		dev_err(wled->dev, "Error in reading WLED3_INT_RT_STS rc=%d\n",
> > > +			rc);
> > > +		return IRQ_HANDLED;
> > > +	}
> > > +
> > > +	rc = regmap_read(wled->regmap, wled->ctrl_addr +
> > > +			 WLED3_CTRL_REG_FAULT_STATUS, &fault_sts);
> > > +	if (rc < 0) {
> > > +		dev_err(wled->dev, "Error in reading WLED_FAULT_STATUS rc=%d\n",
> > > +			rc);
> > > +		return IRQ_HANDLED;
> > > +	}
> > > +
> > > +	if (fault_sts &
> > > +		(WLED3_CTRL_REG_OVP_FAULT_BIT | WLED3_CTRL_REG_ILIM_FAULT_BIT))
> > > +		dev_dbg(wled->dev, "WLED OVP fault detected, int_sts=%x
> > > fault_sts= %x\n",
> > > +			int_sts, fault_sts);
> > > +
> > > +	if (fault_sts & WLED3_CTRL_REG_OVP_FAULT_BIT) {
> > > +		mutex_lock(&wled->lock);
> > > +		disable_irq_nosync(wled->ovp_irq);
> > 
> > We're currently running the threaded ISR for this irq. Do we really need
> > to disable it?
> > 
> We need to disable this IRQ, during the auto string detection logic. Because
> in the auto string detection we configure the current sinks one by one and
> check the
> status register for the OVPs and set the right string configuration. We
> enable it later after
> the auto string detection is completed.

This is a threaded oneshot interrupt handler. Why isn't the framework
masking sufficient for you here?


Daniel.