linux-kernel - Re: [PATCH 5/7] regulator: qcom-labibb: Implement short-circuit and over-current IRQs

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Date:   Mon, 11 Jan 2021 20:23:09 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-arm-msm@...r.kernel.org, agross@...nel.org,
        bjorn.andersson@...aro.org, lgirdwood@...il.com,
        robh+dt@...nel.org, sumit.semwal@...aro.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        phone-devel@...r.kernel.org, konrad.dybcio@...ainline.org,
        marijn.suijten@...ainline.org, martin.botka@...ainline.org
Subject: Re: [PATCH 5/7] regulator: qcom-labibb: Implement short-circuit and
 over-current IRQs

Il 11/01/21 20:14, AngeloGioacchino Del Regno ha scritto:
> Il 11/01/21 14:57, Mark Brown ha scritto:
>> On Sat, Jan 09, 2021 at 02:29:19PM +0100, AngeloGioacchino Del Regno 
>> wrote:
>>
>>> +    /* If the regulator is not enabled, this is a fake event */
>>> +    if (!ops->is_enabled(vreg->rdev))
>>> +        return 0;
>>
>> Or handling the interrupt raced with a disable initiated from elsewhere.
>> Does the hardware actually have a problem with reporting spurious errors?
>>
Sorry, I forgot to answer to this one in the previous email.

Yes, apparently the hardware has this issue: when the current draw is 
very high and you disable the regulator while the attached device is 
still drawing a lot of current (like on the Xperia XZ2 smartphone, but I 
don't want to comment on that phone's HW quirks...) then the OCP 
interrupt fires *after* disabling the LAB/IBB regulators.

This doesn't seem to happen if the current draw is low in the exact 
moment the regulator gets disabled, but that's not always possible since 
it depends on external HW design / board design sometimes...


>>> +    return ret ? IRQ_NONE : IRQ_HANDLED;
>>
>> Here and elsewhere please write normal conditional statements to improve
>> legibility.
>>
> No problem. Will do.
> 
>>> +    /* This function should be called only once, anyway. */
>>> +    if (unlikely(vreg->ocp_irq_requested))
>>> +        return 0;
>>
>> If this is not a fast path it doesn't need an unlikely() annotation;
>> indeed it sounds more like there should be a warning printed if this
>> isn't supposed to be called multiple times.
>>
> That was extra-paranoid safety, looking at this one again, that should 
> be totally unnecessary.
> I think that removing this check entirely would be just fine also 
> because.. anyway.. writing to these registers more than once won't do 
> any harm, nor break functionality: I mean, even if it happens for 
> whatever reason, there's *no real need* to avoid it from the hw 
> perspective.
> 
>>> +    /* IRQ polarities - LAB: trigger-low, IBB: trigger-high */
>>> +    if (vreg->type == QCOM_LAB_TYPE) {
>>> +        irq_flags |= IRQF_TRIGGER_LOW;
>>> +        irq_trig_low = 1;
>>> +    } else {
>>> +        irq_flags |= IRQF_TRIGGER_HIGH;
>>> +        irq_trig_low = 0;
>>> +    }
>>
>> This would be more clearly written as a switch statement.
>>
> A switch statement looked like being a bit "too much" for just two cases 
> where vreg->type cannot be anything else but QCOM_LAB_TYPE or 
> QCOM_IBB_TYPE... but okay, let's write a switch statement in place of that.
> 
>>> +    return devm_request_threaded_irq(vreg->dev, vreg->ocp_irq, NULL,
>>> +                     qcom_labibb_ocp_isr, irq_flags,
>>> +                     ocp_irq_name, vreg);
>>
>> Are you *sure* that devm_ is appropriate here and the interrupt handler
>> won't attempt to use things that will be deallocated before devm gets
>> round to freeing the interrupt?
>>
> Yeah, I'm definitely sure.
> 
>>> +        if (!!(val & LABIBB_CONTROL_ENABLE)) {
>>
>> The !! is redundant here and makes things less clear.
>>
> My bad, I forgot to clean this one up before sending.
> 
>>> @@ -166,8 +560,37 @@ static int qcom_labibb_of_parse_cb(struct 
>>> device_node *np,
>>>                      struct regulator_config *config)
>>>   {
>>>       struct labibb_regulator *vreg = config->driver_data;
>>> +    char *sc_irq_name;
>>
>> I really, really wouldn't expect to see interrupts being requested in
>> the DT parsing callback - apart from anything else the device is going
>> to have the physical interrupts with or without DT binding information.
>> These callbacks are for regulator specific properties, not basic probing.
>> Just request the interrupts in the main probe function, this also means
>> you can avoid using all the DT specific APIs which are generally a
>> warning sign.
>>
> 
> ...And I even wrote a comment saying "The Short Circuit interrupt is 
> critical: fail if not found"!!! Whoa! That was bad.
> Yeah, I'm definitely moving that to the appropriate place.