Re: [PATCH v7 1/9] irqchip: add Amlogic Meson GPIO irqchip driver

[Heiner Kallweit <hkallweit1@gmail.com>]

Am 15.06.2017 um 18:58 schrieb Marc Zyngier:
> On 15/06/17 17:37, Heiner Kallweit wrote:
>> Am 15.06.2017 um 18:04 schrieb Marc Zyngier:
>>> On 15/06/17 16:24, Heiner Kallweit wrote:
>>>> Am 15.06.2017 um 15:27 schrieb Marc Zyngier:
>>>>> On 15/06/17 14:10, Heiner Kallweit wrote:
>>>>>> Am 13.06.2017 um 10:31 schrieb Marc Zyngier:
>>>>>>> On 10/06/17 22:57, Heiner Kallweit wrote:
>>>>>>>> Add a driver supporting the GPIO interrupt controller on certain
>>>>>>>> Amlogic meson SoC's.
>>>>>>>>
>>>>>>>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>>>>>>>> ---
>>>>>>>> v5:
>>>>>>>> - changed Kconfig entry based on Neil's suggestion
>>>>>>>> - added authors
>>>>>>>> - extended explanation why 2 * n hwirqs are used
>>>>>>>> v6:
>>>>>>>> - change DT property parent-interrupts to interrupts
>>>>>>>> v7:
>>>>>>>> - no changes
>>>>>>>> ---
>>>>>>>>  drivers/irqchip/Kconfig          |   5 +
>>>>>>>>  drivers/irqchip/Makefile         |   1 +
>>>>>>>>  drivers/irqchip/irq-meson-gpio.c | 295 +++++++++++++++++++++++++++++++++++++++
>>>>>>>>  3 files changed, 301 insertions(+)
>>>>>>>>  create mode 100644 drivers/irqchip/irq-meson-gpio.c
>>>>>>>>
>>>>>>>> diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
>>>>>>>> index 478f8ace..bdc86e14 100644
>>>>>>>> --- a/drivers/irqchip/Kconfig
>>>>>>>> +++ b/drivers/irqchip/Kconfig
>>>>>>>> @@ -301,3 +301,8 @@ config QCOM_IRQ_COMBINER
>>>>>>>>  	help
>>>>>>>>  	  Say yes here to add support for the IRQ combiner devices embedded
>>>>>>>>  	  in Qualcomm Technologies chips.
>>>>>>>> +
>>>>>>>> +config MESON_GPIO_INTC
>>>>>>>> +	bool
>>>>>>>> +	depends on ARCH_MESON
>>>>>>>> +	default y
>>>>>>>> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
>>>>>>>> index b64c59b8..1be482bd 100644
>>>>>>>> --- a/drivers/irqchip/Makefile
>>>>>>>> +++ b/drivers/irqchip/Makefile
>>>>>>>> @@ -76,3 +76,4 @@ obj-$(CONFIG_EZNPS_GIC)			+= irq-eznps.o
>>>>>>>>  obj-$(CONFIG_ARCH_ASPEED)		+= irq-aspeed-vic.o
>>>>>>>>  obj-$(CONFIG_STM32_EXTI) 		+= irq-stm32-exti.o
>>>>>>>>  obj-$(CONFIG_QCOM_IRQ_COMBINER)		+= qcom-irq-combiner.o
>>>>>>>> +obj-$(CONFIG_MESON_GPIO_INTC)		+= irq-meson-gpio.o
>>>>>>>> diff --git a/drivers/irqchip/irq-meson-gpio.c b/drivers/irqchip/irq-meson-gpio.c
>>>>>>>> new file mode 100644
>>>>>>>> index 00000000..925d00c2
>>>>>>>> --- /dev/null
>>>>>>>> +++ b/drivers/irqchip/irq-meson-gpio.c
>>>>>>>> @@ -0,0 +1,295 @@
>>>>>>>> +/*
>>>>>>>> + * Amlogic Meson GPIO IRQ chip driver
>>>>>>>> + *
>>>>>>>> + * Copyright (c) 2015 Endless Mobile, Inc.
>>>>>>>> + * Author: Carlo Caione <carlo@endlessm.com>
>>>>>>>> + * Copyright (c) 2016 BayLibre, SAS.
>>>>>>>> + * Author: Jerome Brunet <jbrunet@baylibre.com>
>>>>>>>> + * Copyright (c) 2017 Heiner Kallweit <hkallweit1@gmail.com>
>>>>>>>> + *
>>>>>>>> + * This program is free software; you can redistribute it and/or
>>>>>>>> + * modify it under the terms of the GNU General Public License as
>>>>>>>> + * published by the Free Software Foundation, version 2.
>>>>>>>> + */
>>>>>>>> +
>>>>>>>> +#include <linux/device.h>
>>>>>>>> +#include <linux/init.h>
>>>>>>>> +#include <linux/interrupt.h>
>>>>>>>> +#include <linux/irqchip.h>
>>>>>>>> +#include <linux/of.h>
>>>>>>>> +#include <linux/of_irq.h>
>>>>>>>> +#include <linux/of_address.h>
>>>>>>>> +#include <linux/regmap.h>
>>>>>>>> +
>>>>>>>> +#define REG_EDGE_POL		0x00
>>>>>>>> +#define REG_PIN_03_SEL		0x04
>>>>>>>> +#define REG_PIN_47_SEL		0x08
>>>>>>>> +#define REG_FILTER_SEL		0x0c
>>>>>>>> +
>>>>>>>> +#define REG_EDGE_POL_MASK(x)	(BIT(x) | BIT(16 + (x)))
>>>>>>>> +#define REG_EDGE_POL_EDGE(x)	BIT(x)
>>>>>>>> +#define REG_EDGE_POL_LOW(x)	BIT(16 + (x))
>>>>>>>> +
>>>>>>>> +#define MAX_PARENT_IRQ_NUM	8
>>>>>>>> +
>>>>>>>> +/* maximum number of GPIO IRQs on supported platforms */
>>>>>>>> +#define MAX_NUM_GPIO_IRQ	133
>>>>>>>
>>>>>>> Why aren't these values coming from DT? I bet that a future revision of
>>>>>>> the same HW will double these. Or at least, you could match it on the
>>>>>>> compatible string.
>>>>>>>
>>>>>> Alternatively this value can be set to 255. The GPIO source is an 8 bit
>>>>>> value with 255 being reserved for "no interrupt source assigned".
>>>>>
>>>>> Who is reserving it? The HW? Or is that your own defined convention?
>>>>>
>>>>>> This way we cover all chips based on the same IP.
>>>>>
>>>>> Why? Where is that 8bit limit coming from?
>>>>>
>>>> The 8 bit limit is in the HW.
>>>>
>>>>>> I think what we could gain by introducing an additional DT property
>>>>>> (saving a few bytes in the irqdomain mapping table) isn't worth the effort.
>>>>>
>>>>> It is not about saving or wasting memory. It is about making the driver
>>>>> and its binding able to span multiple generation of the HW without too
>>>>> much churn. Which is why I'm suggesting that you either define these
>>>>> properties in DT *or* match the compatible string to obtain these values.
>>>>>
>>>>>>>> +
>>>>>>>> +/*
>>>>>>>> + * In case of IRQ_TYPE_EDGE_BOTH we need two parent interrupts, one for each
>>>>>>>> + * edge. That's due to HW constraints.
>>>>>>>> + * We use format 2 * GPIO_HWIRQ +(0|1) for the hwirq, so we can have one
>>>>>>>> + * GPIO_HWIRQ twice and derive the GPIO_HWIRQ from hwirq by shifting hwirq
>>>>>>>> + * one bit to the right.
>>>>>>>
>>>>>>> Please expand on how you expect this to work, specially when a random
>>>>>>> driver expects a single interrupt.
>>>>>>>
>>>>>> The gpio interrupt controller in this chip doesn't have native support for
>>>>>> IRQ_TYPE_EDGE_BOTH. As a workaround we would need to assign the same gpio
>>>>>> to two parent interrupts, one for each edge.
>>>>>
>>>>> No, that's horrible, racy, and impractical. It has been proposed in the
>>>>> past (for the same HW), and we're not going there again.
>>>>>
>>>> IIRC what has been proposed before is to re-program the polarity of edge
>>>> detection withing the ISR. This would match your concern that it is racy.
>>>>
>>>> Here it's about using two parent irq's, one programmed to react on the
>>>> rising edge whilst the other is triggered in case of falling edge.
>>>> Would you consider this to be racy too?
>>>
>>> How do you reconcile two interrupts to make look like a single one for a
>>> random, pre-existing driver?
>>>
>>> [...]
>>>
>>>>>>> So you reject EDGE_BOTH? So what's the deal with the beginning of the patch?
>>>>>>>
>>>>>> We reject it in the initial version of the patch set as there's no consensus
>>>>>> yet on some details of the workaround needed for EDGE_BOTH support.
>>>>>
>>>>> There is a consensus: The HW doesn't support this feature.
>>>>>
>>>> Means what? There is no acceptable way to support EDGE_BOTH on this HW?
>>>> In this case I could stop here as for me this feature is important.
>>>
>>> Answer my question above, which I asked in my initial review: How do you
>>> make two interrupts appear as one for a driver that wants to get
>>> signaled on each edge, using the existing API.
>>>
>> Please see the pinctrl/gpio part of the patch set.
>>
>> The GPIO controller has an own IRQ domain. When requesting an interrupt
>> in request_resources if needed two parent irq's are allocated, (was removed
>> in the current initial version of the patch set) both calling the same ISR
>> via a chained interrupt.
>>
>> Works perfectly fine here.
> 
> Are you referring to the horror that performs interrupt allocations from
> within the irq_set_type callback? No way. That's beyond disgusting. And
> potentially broken, as the locks that are being taken were never
> designed to nest that way.
> 
No, this horror was the first attempt. In v7 of the patch set this is
done from the request_resources callback.

Rgds, Heiner

> 	M.
>