From: yangyingliang@huawei•com (Yang Yingliang)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] irqchip/gic-v3-its: handle queue wrapping in its_wait_for_range_completion()
Date: Sat, 19 Aug 2017 10:25:26 +0800 [thread overview]
Message-ID: <5997A196.60309@huawei.com> (raw)
In-Reply-To: <ce21378f-c7ad-9a7a-563d-982b1170df93@arm.com>
Hi, Marc
On 2017/8/16 23:12, Marc Zyngier wrote:
> Hi Yang,
>
> On 16/08/17 14:04, Yang Yingliang wrote:
>> If the to_idx wrap to 0, (rd_idx >= to_idx) will be true,
>> but the command is not completed.
>>
>> When to_idx is smaller than from_idx, it means the queue
>> is wrapped. For handling this case, add ITS_CMD_QUEUE_SZ
>> to to_idx and rd_idx to.
>>
>> Signed-off-by: Yang Yingliang <yangyingliang@huawei•com>
>> ---
>> drivers/irqchip/irq-gic-v3-its.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 6893287..8e47515 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -446,13 +446,18 @@ static void its_wait_for_range_completion(struct its_node *its,
>> struct its_cmd_block *to)
>> {
>> u64 rd_idx, from_idx, to_idx;
>> + u32 wrap_offset = 0;
>> u32 count = 1000000; /* 1s! */
>>
>> from_idx = its_cmd_ptr_to_offset(its, from);
>> to_idx = its_cmd_ptr_to_offset(its, to);
>> + if (to_idx < from_idx) {
>> + wrap_offset = ITS_CMD_QUEUE_SZ;
>> + to_idx += ITS_CMD_QUEUE_SZ;
>> + }
>>
>> while (1) {
>> - rd_idx = readl_relaxed(its->base + GITS_CREADR);
>> + rd_idx = readl_relaxed(its->base + GITS_CREADR) + wrap_offset;
>> if (rd_idx >= to_idx || rd_idx < from_idx)
>> break;
>>
>>
>
> I think you've spotted a real issue, but the way you solve it hurts my
> brain. I'd rather have something that makes the cases explicit. Does the
> following work for you?
Yes, it works for me.
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 22e228500357..374977681384 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -453,7 +453,13 @@ static void its_wait_for_range_completion(struct its_node *its,
>
> while (1) {
> rd_idx = readl_relaxed(its->base + GITS_CREADR);
> - if (rd_idx >= to_idx || rd_idx < from_idx)
> +
> + /* Direct case */
> + if (from_idx < to_idx && rd_idx >= to_idx)
> + break;
> +
> + /* Wrapped case */
> + if (from_idx >= to_idx && rd_idx >= to_idx && rd_idx < from_idx)
> break;
>
> count--;
>
> Secondary question: have you seen this breaking in practice? The worse
> case seems that we exit early, and potentially fail to detect a hung
> ITS. But that should never happen, right?
Yes, you are right.
>
> Thanks,
>
> M.
>
prev parent reply other threads:[~2017-08-19 2:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-16 13:04 [PATCH] irqchip/gic-v3-its: handle queue wrapping in its_wait_for_range_completion() Yang Yingliang
2017-08-16 15:12 ` Marc Zyngier
2017-08-19 2:25 ` Yang Yingliang [this message]
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