linux-kernel - Re: [PATCH v4 1/4] genirq: define an empty function set_handle_irq() if !GENERIC_IRQ_MULTI

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Message-ID: <22defc7e8bf8d4dd91565473e1a67f22@kernel.org>
Date:   Thu, 17 Sep 2020 10:32:18 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Rob Herring <robh+dt@...nel.org>, Guo Ren <guoren@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-csky <linux-csky@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Haoyu Lv <lvhaoyu@...wei.com>, Libin <huawei.libin@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Jianguo Chen <chenjianguo3@...wei.com>
Subject: Re: [PATCH v4 1/4] genirq: define an empty function set_handle_irq()
 if !GENERIC_IRQ_MULTI_HANDLER

On 2020-09-17 04:46, Leizhen (ThunderTown) wrote:
> On 2020/9/15 16:43, Zhen Lei wrote:
>> To avoid compilation error if an irqchip driver references the 
>> function
>> set_handle_irq() but may not select GENERIC_IRQ_MULTI_HANDLER on some
>> systems.
> 
> Hi, Marc:
>   Do you agree with this method?
> 
>   Otherwise, I should use "#ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER ... 
> #endif"
> to perform the compilation isolation. This may make the code less 
> beautiful.
> 
>> 
>> For example, the Synopsys DesignWare APB interrupt controller
>> (dw_apb_ictl) is used as the secondary interrupt controller on arc, 
>> csky,
>> arm64, and most arm32 SoCs, and it's also used as the primary 
>> interrupt
>> controller on Hisilicon SD5203 (an arm32 SoC). The latter need to use
>> set_handle_irq() to register the top-level IRQ handler, but this multi
>> irq handler registration mechanism is not implemented on arc system.
>> 
>> The input parameter "handle_irq" maybe defined as static and only
>> set_handle_irq() references it. This will trigger "defined but not 
>> used"
>> warning. So add "(void)handle_irq" to suppress it.
>> 
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> ---
>>  include/linux/irq.h | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/include/linux/irq.h b/include/linux/irq.h
>> index 1b7f4dfee35b397..0848a2aaa9b40b1 100644
>> --- a/include/linux/irq.h
>> +++ b/include/linux/irq.h
>> @@ -1252,6 +1252,8 @@ void irq_matrix_free(struct irq_matrix *m, 
>> unsigned int cpu,
>>   * top-level IRQ handler.
>>   */
>>  extern void (*handle_arch_irq)(struct pt_regs *) __ro_after_init;
>> +#else
>> +#define set_handle_irq(handle_irq)	do { (void)handle_irq; } while (0)
>>  #endif
>> 
>>  #endif /* _LINUX_IRQ_H */
>> 

You shouldn't just make it a NOP. Consider adding a WARN_ON(1), so that
people can realize this cannot work without the required architecture 
support.

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