linux-kernel - Re: [PATCH v4 2/8] irqchip: Add Realtek RTD1295 mux driver

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Date:   Wed, 20 Nov 2019 00:33:28 +0100
From:   Andreas Färber <afaerber@...e.de>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-realtek-soc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Aleix Roca Nonell <kernelrocks@...il.com>,
        James Tai <james.tai@...ltek.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH v4 2/8] irqchip: Add Realtek RTD1295 mux driver

Am 19.11.19 um 23:29 schrieb Marc Zyngier:
> On Tue, 19 Nov 2019 21:56:48 +0100
> Andreas Färber <afaerber@...e.de> wrote:
>> Am 19.11.19 um 13:01 schrieb Marc Zyngier:
>>> On 2019-11-19 02:19, Andreas Färber wrote:  
>>>> +static void rtd1195_mux_enable_irq(struct irq_data *data)
>>>> +{
>>>> +    struct rtd1195_irq_mux_data *mux_data =
>>>> irq_data_get_irq_chip_data(data);
>>>> +    unsigned long flags;
>>>> +    u32 mask;
>>>> +
>>>> +    mask = mux_data->info->isr_to_int_en_mask[data->hwirq];
>>>> +    if (!mask)
>>>> +        return;  
>>>
>>> How can this happen? You've mapped the interrupt, so it exists.
>>> I can't see how you can decide to fail such enable.  
>>
>> The [UMSK_]ISR bits and the SCPU_INT_EN bits are not (all) the same.
>>
>> My ..._isr_to_scpu_int_en[] arrays have 32 entries for O(1) lookup, but
>> are sparsely populated. So there are circumstances such as WDOG_NMI as
>> well as reserved bits that we cannot enable.
> 
> But the you should have failed the map. The moment you allow the
> mapping to occur, you have accepted the contract that this interrupt is
> usable.
> 
>> This check should be
>> identical to v3; the equivalent mask check inside the interrupt handler
>> was extended with "mask &&" to do the same in this v4.
> 
> Spurious interrupts are a different matter. What I'm objecting to here
> is a simple question of logic, whether or not you are allowed to fail
> enabling an interrupt that you've otherwise allowed to be populated.

Then what are you suggesting instead? I don't see how my array map
lookup could fail other than returning a zero value, given its static
initialization. Check for a zero mask in rtd1195_mux_irq_domain_map()?
Then we wouldn't be able to use the mentioned WDOG_NMI. Add another
per-mux info field for which interrupts are valid to map?

Thanks,
Andreas

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