linux-kernel - Re: [PATCH v3 3/3] soundwire: qcom: add in-band wake up interrupt support

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Date:   Tue, 1 Mar 2022 07:51:22 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        robh+dt@...nel.org, vkoul@...nel.org,
        yung-chuan.liao@...ux.intel.com
Cc:     devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, quic_srivasam@...cinc.com
Subject: Re: [PATCH v3 3/3] soundwire: qcom: add in-band wake up interrupt
 support



On 3/1/22 05:13, Srinivas Kandagatla wrote:
> 
> 
> On 28/02/2022 18:01, Pierre-Louis Bossart wrote:
>>
>>> @@ -1424,6 +1464,11 @@ static int swrm_runtime_resume(struct device
>>> *dev)
>>>       struct qcom_swrm_ctrl *ctrl = dev_get_drvdata(dev);
>>>       int ret;
>>>   +    if (ctrl->wake_irq > 0) {
>>> +        if (!irqd_irq_disabled(irq_get_irq_data(ctrl->wake_irq)))
>>> +            disable_irq_nosync(ctrl->wake_irq);
>>> +    }
>>> +
>>>       clk_prepare_enable(ctrl->hclk);
>>
>> This one is quite interesting. If you disable the IRQ mechanism but
>> haven't yet resumed the clock, that leaves a time window where the
>> peripheral could attempt to drive the line high. what happens in that
>> case?
> 
> 
> We did call pm_runtime_get_sync() from Wake IRQ handler, which means
> that resume should be finished as part of Wake IRQ handler. Any new
> Interrupt conditions/status generated by slave in the meantime will be
> cleared while handling SLAVE PEND interrupt.
> 
>>
>>>         if (ctrl->clock_stop_not_supported) {
>>> @@ -1491,6 +1536,11 @@ static int __maybe_unused
>>> swrm_runtime_suspend(struct device *dev)
>>>         usleep_range(300, 305);
>>>   +    if (ctrl->wake_irq > 0) {
>>> +        if (irqd_irq_disabled(irq_get_irq_data(ctrl->wake_irq)))
>>> +            enable_irq(ctrl->wake_irq);
>>> +    }
>>> +
>>
>> and this one is similar, you could have a case where the peripheral
>> signals a wake immediately after the ClockStopNow frame, but you may not
>> yet have enabled the wake detection interrupt.
>>
>> Would that imply that the wake is missed?
> Its Possible it might be missed at that instance, however as the Slave
> interrupt source condition/status (Ex: button Press) is still not
> cleared it should generate a Wake interrupt as soon as its enabled.

ok, thanks for the answers - both make sense.