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

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Date:   Wed, 20 Nov 2019 10:20:20 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Andreas Färber <afaerber@...e.de>
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

On 2019-11-19 23:33, Andreas Färber wrote:
> 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?

I'm suggesting that you fail the map if you're unable to allow the
interrupt to be enabled.

         M.
-- 
Jazz is not dead. It just smells funny...