linux-kernel - Re: [PATCH v4 5/5] regulator: qcom: labibb: Add SC interrupt handling

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Message-ID: <CAO_48GGY2TRVPXFVCvo9fEoknw65sz9BrL-mp+SZ=_EAo88t-A@mail.gmail.com>
Date:   Wed, 17 Jun 2020 17:36:43 +0530
From:   Sumit Semwal <sumit.semwal@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     agross@...nel.org, Bjorn Andersson <bjorn.andersson@...aro.org>,
        lgirdwood@...il.com, robh+dt@...nel.org,
        Nisha Kumari <nishakumari@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, kgunda@...eaurora.org,
        Rajendra Nayak <rnayak@...eaurora.org>
Subject: Re: [PATCH v4 5/5] regulator: qcom: labibb: Add SC interrupt handling

Hi Mark,

On Tue, 2 Jun 2020 at 17:52, Mark Brown <broonie@...nel.org> wrote:
>
> On Tue, Jun 02, 2020 at 03:39:24PM +0530, Sumit Semwal wrote:
>
> >  static int qcom_labibb_regulator_enable(struct regulator_dev *rdev)
> >  {
> > -     return regulator_enable_regmap(rdev);
> > +     int ret;
> > +     struct labibb_regulator *reg = rdev_get_drvdata(rdev);
> > +
> > +     ret = regulator_enable_regmap(rdev);
> > +     if (ret >= 0)
> > +             reg->enabled = true;
>
> Can we not read the register we just wrote to here?
As I mentioned in the other patch, it seems there is a (noticeable)
delay in getting the value to reflect in this register for IBB.

Also, from the notes from the downstream driver (also copied below),
it seems like during short circuit there is another protection system
that can cause the registers to be cleared, hence the need to track
the current state in software.

>
> > +     /*
> > +      * The SC(short circuit) fault would trigger PBS(Portable Batch
> > +      * System) to disable regulators for protection. This would
> > +      * cause the SC_DETECT status being cleared so that it's not
> > +      * able to get the SC fault status.
> > +      * Check if the regulator is enabled in the driver but
> > +      * disabled in hardware, this means a SC fault had happened
> > +      * and SCP handling is completed by PBS.
> > +      */
> > +     if (!in_sc_err) {
> > +
> > +             reg = labibb_reg->base + REG_LABIBB_ENABLE_CTL;
> > +
> > +             ret = regmap_read_poll_timeout(labibb_reg->regmap,
> > +                                     reg, val,
> > +                                     !(val & LABIBB_CONTROL_ENABLE),
> > +                                     POLLING_SCP_DONE_INTERVAL_US,
> > +                                     POLLING_SCP_TIMEOUT);
>
> Why do we need a timeout here?
IMHO, This seems to be the time required by the PBS to actually
disable the regulator? If the PBS is not able to disable the
regulator, then it points to a more serious problem?
I'm sorry, that's just my understanding based on the downstream driver
:/ - not much input is available from the QC teams about it.

>
> > +                                             NULL);
> > +             regulator_unlock(labibb_reg->rdev);
> > +     }
> > +     return IRQ_HANDLED;
>
> This returns IRQ_HANDLED even if we didn't detect an interrupt source...
> Especially given the need to check to see if the regulator was turned
> off by the hardware it seems like there must be some false positives.
Right - I'm not sure what else can I do here.
>
> > +     } else {
> > +             ret = devm_request_threaded_irq(reg->dev,
> > +                                             sc_irq,
> > +                                             NULL, labibb_sc_err_handler,
> > +                                             IRQF_ONESHOT,
> > +                                             "sc-err", reg);
>
> This looks like we're requesting the interrupt before we register the
> regulator which means the interrupt might fire without the regulator
> being there.  The order of registration should be reversed.

Agreed, and will update in the next version.

Best,
Sumit.