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

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Message-ID: <01570d5d-0bdf-4192-a703-88854e9bcf78@redhat.com>
Date: Mon, 14 Apr 2025 13:04:46 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: "Yan, Dongcheng" <dongcheng.yan@...el.com>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.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,

On 14-Apr-25 11:59, Yan, Dongcheng wrote:
> 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?

Yes that is acceptable, thank you for looking this up.

Regards,

Hans



> 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.
>>
>