linux-kernel - Re: [PATCH v1 1/2] platform/x86: int3472: add hpd pin support

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Message-ID: <Z_zMyodMQoH6EtSR@kekkonen.localdomain>
Date: Mon, 14 Apr 2025 08:52:26 +0000
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: "Yan, Dongcheng" <dongcheng.yan@...ux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Dongcheng Yan <dongcheng.yan@...el.com>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	hverkuil@...all.nl, u.kleine-koenig@...libre.com,
	ricardo.ribalda@...il.com, bingbu.cao@...ux.intel.com,
	hao.yao@...el.com
Subject: Re: [PATCH v1 1/2] platform/x86: int3472: add hpd pin support

Hi Dongcheng,

On Mon, Apr 14, 2025 at 04:40:26PM +0800, Yan, Dongcheng wrote:
> Hi Andy,
> 
> On 4/14/2025 4:11 PM, Andy Shevchenko wrote:
> > On Mon, Apr 14, 2025 at 03:52:50PM +0800, Yan, Dongcheng wrote:
> >> On 4/11/2025 4:33 PM, Hans de Goede wrote:
> >>> On 11-Apr-25 10:23 AM, Dongcheng Yan wrote:
> > 
> > ...
> > 
> >>>> +	case INT3472_GPIO_TYPE_HOTPLUG_DETECT:
> >>>> +		*con_id = "hpd";
> >>>> +		*gpio_flags = GPIO_LOOKUP_FLAGS_DEFAULT;
> >>>
> >>> This looks wrong, we really need to clearly provide a polarity
> >>> here since the ACPI GPIO resources do not provide one.
> >>>
> >> I tested gpio_flags=GPIO_LOOKUP_FLAGS_DEFAULT/HIGH/LOW, the lt6911uxe
> >> driver can pass the test and work normally.
> > 
> > I doubt you tested that correctly. It's impossible to have level triggered
> > event to work with either polarity. It might be also a bug in the code lurking
> > somewhere, but it would be unlikely (taking into account amount of systems
> > relying on this).
> > 
> > Is it edge triggered event?
> > 
> 
> It is an edge triggered event in lt6911uxe. In order to better adapt to
> other uses, "hpd" is meaningful to specify a polarity here.
> 
> In lt6911uxe, GPIO "hpd" is used as irq, and set irq-flag to
> IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING | IRQF_ONESHOT. So no matter
> rising or falling, driver can work normally.
> "
> ret = request_threaded_irq(gpiod_to_irq(lt6911uxe->irq_gpio),	NULL,
> lt6911uxe_threaded_irq_fn, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING |
> IRQF_ONESHOT, NULL, lt6911uxe);
> "

include/linux/gpio/machine.h:

	GPIO_PERSISTENT                 = (0 << 3),
...
	GPIO_LOOKUP_FLAGS_DEFAULT       = GPIO_ACTIVE_HIGH | GPIO_PERSISTENT,

I.e. you effectively have GPIO_ACTIVE_HIGH there.

Btw. no need to cc this set to stable@...r.kernel.org, I've dropped it from
the cc list. See Documentation/process/submitting-patches.rst .

-- 
Regards,

Sakari Ailus