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Message-ID: <54F677BF.9060208@huawei.com>
Date: Wed, 4 Mar 2015 11:10:55 +0800
From: "Yun Wu (Abel)" <wuyun.wu@...wei.com>
To: Marc Zyngier <marc.zyngier@....com>
CC: "tglx@...utronix.de" <tglx@...utronix.de>,
"jason@...edaemon.net" <jason@...edaemon.net>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] irqchip: gicv3-its: add support for power down
On 2015/2/17 20:27, Yun Wu (Abel) wrote:
> On 2015/2/17 19:11, Marc Zyngier wrote:
>
>> On Tue, 17 Feb 2015 10:15:15 +0000
>> "Yun Wu (Abel)" <wuyun.wu@...wei.com> wrote:
>>
>>> On 2015/2/17 17:29, Marc Zyngier wrote:
>>>
>>>> On Sun, 15 Feb 2015 09:32:02 +0000
>>>> Yun Wu <wuyun.wu@...wei.com> wrote:
>>>>
>>>>> It's unsafe to change the configurations of an activated ITS
>>>>> directly since this will lead to unpredictable results. This patch
>>>>> guarantees a safe quiescent status before initializing an ITS.
>>>>
>>>> Please change the title of this patch to reflect what it actually
>>>> does. Nothing here is about powering down anything.
>>>
>>> My miss, I will fix this in next version.
>>>
>>>>
>>>>> Signed-off-by: Yun Wu <wuyun.wu@...wei.com>
>>>>> ---
>>>>> drivers/irqchip/irq-gic-v3-its.c | 32
>>>>> ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)
>>>>>
>>>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c
>>>>> b/drivers/irqchip/irq-gic-v3-its.c index 42c03b2..29eb665 100644
>>>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>>>> @@ -1321,6 +1321,31 @@ static const struct irq_domain_ops
>>>>> its_domain_ops = { .deactivate =
>>>>> its_irq_domain_deactivate, };
>>>>>
>>>>> +static int its_check_quiesced(void __iomem *base)
>>>>> +{
>>>>> + u32 count = 1000000; /* 1s */
>>>>> + u32 val;
>>>>> +
>>>>> + val = readl_relaxed(base + GITS_CTLR);
>>>>> + if (val & GITS_CTLR_QUIESCENT)
>>>>> + return 0;
>>>>> +
>>>>> + /* Disable the generation of all interrupts to this ITS */
>>>>> + val &= ~GITS_CTLR_ENABLE;
>>>>> + writel_relaxed(val, base + GITS_CTLR);
>>>>> +
>>>>> + /* Poll GITS_CTLR and wait until ITS becomes quiescent */
>>>>> + while (count--) {
>>>>> + val = readl_relaxed(base + GITS_CTLR);
>>>>> + if (val & GITS_CTLR_QUIESCENT)
>>>>> + return 0;
>>>>> + cpu_relax();
>>>>> + udelay(1);
>>>>> + }
>>>>
>>>> You're now introducing a third variant of a 1s timeout loop. Notice
>>>> a pattern?
>>>>
>>>
>>> I am not sure I know exactly what you suggest. Do you mean I should
>>> code like below to keep the coding style same as the other 2 loops?
>>>
>>> while (1) {
>>> val = readl_relaxed(base + GITS_CTLR);
>>> if (val & GITS_CTLR_QUIESCENT)
>>> return 0;
>>>
>>> count--;
>>> if (!count)
>>> return -EBUSY;
>>>
>>> cpu_relax();
>>> udelay(1);
>>> }
>>
>> That'd be a good start. But given that this is starting to be a common
>> construct, it could probably be rewritten as:
>>
>> static int its_poll_timeout(struct its_node *its, void *data,
>> int (*fn)(struct its_node *its,
>> void *data))
>> {
>> while (1) {
>> if (!fn(its, data))
>> return 0;
>>
>> ...
>> }
>> }
>>
>> and have the call sites to provide the right utility function. We also
>> have two similar timeout loops in the main GICv3 driver, so there
>> should be room for improvement.
>>
>> Thoughts?
>>
Hi Marc,
Currently I didn't make any improvement on providing a unified utility
function to do the timeout loops, because I haven't found a proper way
yet. And to achieve this, at least three aspects I can imagine are
needed to be considered.
Refactoring the existing loop functions comes first. A prototype is
showed below.
static T1 func_prototype(T2 node, char *msg, void **args)
{
u32 count = 1000000;
do_something_here(node, args);
while (1) {
if (condition_satisfied(node, args))
return (T1)SUCCESS;
count--;
if (!count) {
print_err_msg(msg);
return (T1)FAIL;
}
cpu_relax();
udelay(1);
}
}
Obviously it will make things complicated to move do_something_here() and
print_err_msg() outside of func_prototype(), because func_prototype() could
be called sereval places. But the two functions are different from each
loop function, so...
static T1 func_prototype(T2 node, char *msg, void **args)
{
u32 count = 1000000;
do_something_here(node, args);
while (count--) {
if (condition_satisfied(node, args))
return (T1)SUCCESS;
cpu_relax();
udelay(1);
}
print_err_msg(msg);
return (T1)FAIL;
}
Now we can unify the loop part,
static bool condition_satisfied(T2 node, void **args);
static u32 poll_timeout(T2 node, void **args,
bool (*fn)(T2, void **))
{
u32 count = 1000000;
while (count--) {
if (fn(node, args))
break;
cpu_relax();
udelay(1);
}
return count;
}
static T1 func_prototype(T2 node, char *msg, void **args)
{
do_something_here(node, args);
if (poll_timeout(node, args, condition_satisfied)) {
return (T1)SUCCESS;
} else {
print_err_msg(msg);
return (T1)FAIL;
}
}
Look at what I have done, turn the original N loop functions to 2*N+1 functions.
It can hardly be called improvement.. :(
The 2nd and 3rd aspects are return value and list of parameters respectively.
Using (void *) may help a lot, I think.
Thoughts?
Thanks,
Abel
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