linux-kernel - Re: [PATCH 3/3] irqchip: dw-apb-ictl: add PM support

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Date:	Wed, 08 Oct 2014 13:44:49 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Jisheng Zhang <jszhang@...vell.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	"jason@...edaemon.net" <jason@...edaemon.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] irqchip: dw-apb-ictl: add PM support

On 10/08/2014 01:31 PM, Jisheng Zhang wrote:
> Hi Thomas, Sebastian,
>
> On Tue, 30 Sep 2014 14:52:54 -0700
> Thomas Gleixner <tglx@...utronix.de> wrote:
>
>> On Tue, 30 Sep 2014, Sebastian Hesselbarth wrote:
>>> On 09/23/2014 08:35 AM, Jisheng Zhang wrote:
>>>> This patch adds in support for S2R for dw-apb-ictl irqchip driver.
>>>>
>>>> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
>>>> ---
>>>>    drivers/irqchip/irq-dw-apb-ictl.c | 19 +++++++++++++++++++
>>>>    1 file changed, 19 insertions(+)
>>>>
>>>> diff --git a/drivers/irqchip/irq-dw-apb-ictl.c
>>>> b/drivers/irqchip/irq-dw-apb-ictl.c
>>>> index c136b67..53bb732 100644
>>>> --- a/drivers/irqchip/irq-dw-apb-ictl.c
>>>> +++ b/drivers/irqchip/irq-dw-apb-ictl.c
>>>> @@ -50,6 +50,21 @@ static void dw_apb_ictl_handler(unsigned int irq,
>>>> struct irq_desc *desc)
>>>>    	chained_irq_exit(chip, desc);
>>>>    }
>>>>
>>>> +#ifdef CONFIG_PM
>>>> +static void dw_apb_ictl_resume(struct irq_data *d)
>>>> +{
>>>> +	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(d);
>>>> +	struct irq_chip_type *ct = irq_data_get_chip_type(d);
>>>> +
>>>> +	irq_gc_lock(gc);
>>>> +	writel_relaxed(~0, gc->reg_base + ct->regs.enable);
>>>> +	writel_relaxed(*ct->mask_cache, gc->reg_base + ct->regs.mask);
>>>> +	irq_gc_unlock(gc);
>>>> +}
>>>
>>> I agree with the overall change, but may this also be suited for a
>>> generic irq_chip helper instead of being a driver specific one?
>>>
>>> Maybe Thomas or Jason can comment on this.
>>
>> If we have enough similar resume callbacks, yes.
>>
>>> Also, now that you are using writel_relaxed, I understand that both
>>> writes above can happen in any order? Are there any implication we
>>> have to consider, i.e. do we require any of the registers above to
>>> be written first?
>
> The registers sits at device type memory, the writes should happen in the same
> order as before.

Jisheng,

it is not about the location of the register but, as far as I
understand, when using {readl,writel}_relaxed the compiler is
free to reorder the calls. So, if there is a strict order we
want to ensure, we have to use non-relaxed {readl,writel}.

The performance penalty of non-relaxed calls can be ignored anyway
as it is done only once after resume.

Sebastian
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