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

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Message-ID: <f10f919e-7bdc-4a01-b131-41bdc9eb6573@intel.com>
Date: Mon, 14 Apr 2025 17:59:13 +0800
From: "Yan, Dongcheng" <dongcheng.yan@...el.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Hans de Goede <hdegoede@...hat.com>,
 "Yan, Dongcheng" <dongcheng.yan@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 sakari.ailus@...ux.intel.com, hverkuil@...all.nl,
 u.kleine-koenig@...libre.com, ricardo.ribalda@...il.com,
 bingbu.cao@...ux.intel.com, stable@...r.kernel.org, hao.yao@...el.com
Subject: Re: [PATCH v1 1/2] platform/x86: int3472: add hpd pin support

Hi Andy and Hans,

I found the description of lt6911uxe's GPIO in the spec:
GPIO5 is used as the interrupt signal (50ms low level) to inform SOC
start reading registers from 6911UXE;

So setting the polarity as GPIO_ACTIVE_LOW is acceptable?
We used RISING and FALLING in irq(not GPIO) to ensure that HDMI events
will not be lost to the greatest extent possible.

Thanks,
Dongcheng

On 4/14/2025 4:49 PM, Andy Shevchenko wrote:
> On Mon, Apr 14, 2025 at 04:40:26PM +0800, Yan, Dongcheng wrote:
>> 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);
>> "
> 
> So, the driver must not override the firmware, if there is no bugs.
> So, why do you even use those flags there? It seems like a bad code
> in the driver that doesn't look correct to me.
>