Message-ID: <1f8f7b9f-7788-18c4-19c5-3c9a7623c188@arm.com>
Date:   Thu, 10 Nov 2016 18:24:07 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Youlin Pei <youlin.pei@...iatek.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        hongkun.cao@...iatek.com, yong.wu@...iatek.com,
        erin.lo@...iatek.com, chieh-jay.liu@...iatek.com
Subject: Re: [PATCH v2 2/3] irqchip: mtk-cirq: Add mediatek mtk-cirq implement

On 08/11/16 02:57, Youlin Pei wrote:
> On Fri, 2016-11-04 at 22:21 +0000, Marc Zyngier wrote:
>> On Fri, Nov 04 2016 at 04:42:57 AM, Youlin Pei <youlin.pei@...iatek.com> wrote:
>>> On Tue, 2016-11-01 at 20:49 +0000, Marc Zyngier wrote:
>>>> On Tue, Nov 01 2016 at 11:52:01 AM, Youlin Pei <youlin.pei@...iatek.com> wrote:
>>>>> In Mediatek SOCs, the CIRQ is a low power interrupt controller
>>>>> designed to works outside MCUSYS which comprises with Cortex-Ax
>>>>> cores,CCI and GIC.
>>>>>
>>>>> The CIRQ controller is integrated in between MCUSYS( include
>>>>> Cortex-Ax, CCI and GIC ) and interrupt sources as the second
>>>>> level interrupt controller. The external interrupts which outside
>>>>> MCUSYS will feed through CIRQ then bypass to GIC. CIRQ can monitors
>>>>> all edge trigger interupts. When an edge interrupt is triggered,
>>>>> CIRQ can record the status and generate a pulse signal to GIC when
>>>>> flush command executed.
>>>>>
>>>>> When system enters sleep mode, MCUSYS will be turned off to improve
>>>>> power consumption, also GIC is power down. The edge trigger interrupts
>>>>> will be lost in this scenario without CIRQ.
>>>>>
>>>>> This commit provides the CIRQ irqchip implement.
>>>>>
>>>>> Signed-off-by: Youlin Pei <youlin.pei@...iatek.com>
>>>>> ---
>>>>>  drivers/irqchip/Makefile       |    2 +-
>>>>>  drivers/irqchip/irq-mtk-cirq.c |  262 ++++++++++++++++++++++++++++++++++++++++
>>>>>  2 files changed, 263 insertions(+), 1 deletion(-)
>>>>>  create mode 100644 drivers/irqchip/irq-mtk-cirq.c
>>>>>
>>>>> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
>>>>> index e4dbfc8..8f33580 100644
>>>>> --- a/drivers/irqchip/Makefile
>>>>> +++ b/drivers/irqchip/Makefile
>>>>> @@ -60,7 +60,7 @@ obj-$(CONFIG_BCM7120_L2_IRQ)		+= irq-bcm7120-l2.o
>>>>>  obj-$(CONFIG_BRCMSTB_L2_IRQ)		+= irq-brcmstb-l2.o
>>>>>  obj-$(CONFIG_KEYSTONE_IRQ)		+= irq-keystone.o
>>>>>  obj-$(CONFIG_MIPS_GIC)			+= irq-mips-gic.o
>>>>> -obj-$(CONFIG_ARCH_MEDIATEK)		+= irq-mtk-sysirq.o
>>>>> +obj-$(CONFIG_ARCH_MEDIATEK)		+= irq-mtk-sysirq.o irq-mtk-cirq.o
>>>>>  obj-$(CONFIG_ARCH_DIGICOLOR)		+= irq-digicolor.o
>>>>>  obj-$(CONFIG_RENESAS_H8300H_INTC)	+= irq-renesas-h8300h.o
>>>>>  obj-$(CONFIG_RENESAS_H8S_INTC)		+= irq-renesas-h8s.o
>>>>> diff --git a/drivers/irqchip/irq-mtk-cirq.c b/drivers/irqchip/irq-mtk-cirq.c
>>>>> new file mode 100644
>>>>> index 0000000..fc43ef3
>>>>> --- /dev/null
>>>>> +++ b/drivers/irqchip/irq-mtk-cirq.c
>>>>> @@ -0,0 +1,262 @@
>>>>> +/*
>>>>> + * Copyright (c) 2016 MediaTek Inc.
>>>>> + * Author: Youlin.Pei <youlin.pei@...iatek.com>
>>>>> + *
>>>>> + * This program is free software; you can redistribute it and/or modify
>>>>> + * it under the terms of the GNU General Public License version 2 as
>>>>> + * published by the Free Software Foundation.
>>>>> + *
>>>>> + * This program is distributed in the hope that it will be useful,
>>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>>> + * GNU General Public License for more details.
>>>>> + */
>>>>> +
>>>>> +#include <linux/irq.h>
>>>>> +#include <linux/irqchip.h>
>>>>> +#include <linux/irqdomain.h>
>>>>> +#include <linux/of.h>
>>>>> +#include <linux/of_irq.h>
>>>>> +#include <linux/of_address.h>
>>>>> +#include <linux/io.h>
>>>>> +#include <linux/slab.h>
>>>>> +#include <linux/syscore_ops.h>
>>>>> +
>>>>> +#define CIRQ_ACK	0x40
>>>>> +#define CIRQ_MASK_SET	0xc0
>>>>> +#define CIRQ_MASK_CLR	0x100
>>>>> +#define CIRQ_SENS_SET	0x180
>>>>> +#define CIRQ_SENS_CLR	0x1c0
>>>>> +#define CIRQ_POL_SET	0x240
>>>>> +#define CIRQ_POL_CLR	0x280
>>>>> +#define CIRQ_CONTROL	0x300
>>>>> +
>>>>> +#define CIRQ_EN	0x1
>>>>> +#define CIRQ_EDGE	0x2
>>>>> +#define CIRQ_FLUSH	0x4
>>>>> +
>>>>> +#define CIRQ_IRQ_NUM    0x200
>>>>> +
>>>>> +struct mtk_cirq_chip_data {
>>>>> +	void __iomem *base;
>>>>> +	unsigned int ext_irq_start;
>>>>> +};
>>>>> +
>>>>> +static struct mtk_cirq_chip_data *cirq_data;
>>>>
>>>> Are you guaranteed that you'll only ever have a single CIRQ in any
>>>> system?
>>>
>>> In Mediatek's SOC, only hace a single CIRQ.
>>>
>>>>
>>>>> +
>>>>> +static void mtk_cirq_write_mask(struct irq_data *data, unsigned int offset)
>>>>> +{
>>>>> +	struct mtk_cirq_chip_data *chip_data = data->chip_data;
>>>>> +	unsigned int cirq_num = data->hwirq;
>>>>> +	u32 mask = 1 << (cirq_num % 32);
>>>>> +
>>>>> +	writel(mask, chip_data->base + offset + (cirq_num / 32) * 4);
>>>>
>>>> Why can't you use the relaxed accessors?
>>>
>>> It seems that i use wrong function, i will change the writel to
>>> writel_relaxed in next ve
>>>
>>>>
>>>>> +}
>>>>> +
>>>>> +static void mtk_cirq_mask(struct irq_data *data)
>>>>> +{
>>>>> +	mtk_cirq_write_mask(data, CIRQ_MASK_SET);
>>>>> +	irq_chip_mask_parent(data);
>>>>> +}
>>>>> +
>>>>> +static void mtk_cirq_unmask(struct irq_data *data)
>>>>> +{
>>>>> +	mtk_cirq_write_mask(data, CIRQ_MASK_CLR);
>>>>> +	irq_chip_unmask_parent(data);
>>>>> +}
>>>>> +
>>>>> +static void mtk_cirq_eoi(struct irq_data *data)
>>>>> +{
>>>>> +	mtk_cirq_write_mask(data, CIRQ_ACK);
>>>>
>>>> EOI and ACK have very different semantics. What is this write actually
>>>> doing? Also, you're now doing an additional MMIO write on each interrupt
>>>> EOI, doubling its cost. Do you really need to do actually signal the HW
>>>> that we've EOIed an interrupt? I would have hoped that you'd be able to
>>>> put it in "bypass" mode as long as you're not suspending...
>>>>
>>>
>>> When external interrupt happened, CIRQ status register record the status
>>> even CIRQ is not enabled. when execute the flush command, CIRQ will
>>> resend the signals according to the status. So if don't clear the
>>> status, CIRQ will resend the wrong signals. the ACK write operation will
>>> clear the status.
>>
>> But at this time, we haven't suspended yet, and there is nothing to
>> replay. Also, you only enable the edge capture when suspending. So what
>> are you ACKing here? Can't you simply clear everything right when
>> suspending and not do it at all on the fast path?
> 
> I had planned to ACK the status in cirq suspend callback, but
> encountered a problem.
> following is a piece of code from
> http://lxr.free-electrons.com/source/kernel/power/suspend.c#L361
> 
> arch_suspend_disable_irqs(); ---step1
> BUG_ON(!irqs_disabled());
> 
> error = syscore_suspend();
>            |
>            ---cirq suspend(); ---step2
> 
> if ack the status in cirq suspend, the interrupts will be lost which
> happened during step1 to step2.
> 
> So would you mind give me some suggestions about this?
> Thanks a lot!

Right. So maybe there is a way:
- On suspend you can iterate over all the cirq interrupts that have been
recorded
- For each of those, you inspect if it is pending at the GIC level
(using the irq_get_irqchip_state helper)
- if not pending, you Ack it, because it cannot be delivered anymore
- If it is pending, then you know it happened between step 1 and step 2.
- You then have the choice of either going into suspend and waking up
immediately, or failing the suspend.

Thoughts?

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

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