Re: [PATCH v4 16/19] thermal/drivers/tegra: Remove unneeded lock when setting a trip point

Daniel Lezcano
2023-03-02T10:11:35Z

On 02/03/2023 10:45, Thierry Reding wrote:

[ ... ]

>>>> + /*
>>>> + * Disable the interrupt so set_trips() can not be called
>>>> + * while we are setting up the register
>>>> + * TSENSOR_SENSOR0_CONFIG1. With this we close a potential
>>>> + * race window where we are setting up the TH2 and the
>>>> + * temperature hits TH1 resulting to an update of the
>>>> + * TSENSOR_SENSOR0_CONFIG1 register in the ISR.
>>>> + */
>>>> + disable_irq(irq);
>>>> +
>>>> for (i = 0; i < ARRAY_SIZE(ts->ch); i++) {
>>>> err = tegra_tsensor_enable_hw_channel(ts, i);
>>>> if (err)
>>>> return err;
>>>> }
>>>> + enable_irq(irq);
>>>
>>> Instead of disabling and reenabling the interrupt, could we simply move
>>> the channel enabling code a couple of lines above, before the IRQ
>>> request call? If enabling the channels were to trigger an interrupt, it
>>> should get triggered right after requesting the IRQ.
>>
>> Won't we have a spurious interrupt if that situation happen ?
>
> It wouldn't be a spurious interrupt, but rather something that we want
> to react to. It's ultimately the same result as your patch. In your
> variant we basically request the IRQ (which automatically enables it),
> then immediately disable it, enable the HW channels and then reenable
> the interrupt. If enabling the HW channels were to trigger an interrupt,
> that interrupt would be raised immediately after enable_irq() as well,
> as far as I can tell.

I see, thanks for the clarification

-- Daniel

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