linux-kernel - Re: [PATCH] irqchip: stm32: don't set rising configuration registers at init

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Message-ID: <bd9a176c-42cc-1238-0578-4c994c864151@arm.com>
Date:   Thu, 7 Mar 2019 17:46:06 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Fabien DESSENNE <fabien.dessenne@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Cc:     Benjamin GAIGNARD <benjamin.gaignard@...com>
Subject: Re: [PATCH] irqchip: stm32: don't set rising configuration registers
 at init

On 07/03/2019 17:24, Fabien DESSENNE wrote:
> Hi
> 
> 
>> -----Original Message-----
>> From: Marc Zyngier <marc.zyngier@....com>
>> Sent: jeudi 7 mars 2019 17:40
>> To: Fabien DESSENNE <fabien.dessenne@...com>; Thomas Gleixner
>> <tglx@...utronix.de>; Jason Cooper <jason@...edaemon.net>; Maxime Coquelin
>> <mcoquelin.stm32@...il.com>; Alexandre TORGUE
>> <alexandre.torgue@...com>; linux-kernel@...r.kernel.org; linux-stm32@...md-
>> mailman.stormreply.com; linux-arm-kernel@...ts.infradead.org
>> Cc: Benjamin GAIGNARD <benjamin.gaignard@...com>
>> Subject: Re: [PATCH] irqchip: stm32: don't set rising configuration registers at init
>>
>> On 07/03/2019 16:15, Fabien Dessenne wrote:
>>> The rising configuration status register (rtsr) is not banked.
>>> As it is shared with the co-processor, it should not be written at
>>> probe time, else the co-processor configuration will be lost.
>>>
>>> Signed-off-by: Fabien Dessenne <fabien.dessenne@...com>
>>
>> Fixes:?
>>
>>> ---
>>>  drivers/irqchip/irq-stm32-exti.c | 5 -----
>>>  1 file changed, 5 deletions(-)
>>>
>>> diff --git a/drivers/irqchip/irq-stm32-exti.c
>>> b/drivers/irqchip/irq-stm32-exti.c
>>> index 6edfd4b..ff8a84f 100644
>>> --- a/drivers/irqchip/irq-stm32-exti.c
>>> +++ b/drivers/irqchip/irq-stm32-exti.c
>>> @@ -716,7 +716,6 @@ stm32_exti_chip_data *stm32_exti_chip_init(struct
>> stm32_exti_host_data *h_data,
>>>  	const struct stm32_exti_bank *stm32_bank;
>>>  	struct stm32_exti_chip_data *chip_data;
>>>  	void __iomem *base = h_data->base;
>>> -	u32 irqs_mask;
>>>
>>>  	stm32_bank = h_data->drv_data->exti_banks[bank_idx];
>>>  	chip_data = &h_data->chips_data[bank_idx]; @@ -725,10 +724,6 @@
>>> stm32_exti_chip_data *stm32_exti_chip_init(struct stm32_exti_host_data
>>> *h_data,
>>>
>>>  	raw_spin_lock_init(&chip_data->rlock);
>>>
>>> -	/* Determine number of irqs supported */
>>> -	writel_relaxed(~0UL, base + stm32_bank->rtsr_ofst);
>>> -	irqs_mask = readl_relaxed(base + stm32_bank->rtsr_ofst);
>>> -
>>
>> And I guess you don't need to find out the number of supported IRQs?
> 
> That's correct, this informed is useless : irqs_mask is never used (it used to be output in a log for debug purpose.and the log has been removed)
> 
> 
>>
>> Also, a handful of lines down, you're writing again to the same register. Why isn't
>> that a problem?
> 
> It's obviously a problem : another patch is missing, I am going to add it in v2.
> Thanks for pointing this out!

You are also happily writing to that register in other places via
stm32_exti_set_bit and co. All that is done without any cooperation with
the coprocessor (whatever that is...), so I really wonder if it all
works by magic or luck...

Thanks,

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