linux-kernel - Re: [PATCH v13 3/3] Input: Add TouchNetix axiom i2c touchscreen driver

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Message-ID: <87bk4dfc7b.fsf@BLaptop.bootlin.com>
Date: Fri, 07 Jun 2024 09:23:36 +0200
From: Gregory CLEMENT <gregory.clement@...tlin.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>, Kamel BOUHARA
 <kamel.bouhara@...tlin.com>
Cc: Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>,
 Henrik Rydberg <rydberg@...math.org>, linux-input@...r.kernel.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, Marco Felsch
 <m.felsch@...gutronix.de>, Jeff LaBundy <jeff@...undy.com>,
 catalin.popescu@...ca-geosystems.com, mark.satterthwaite@...chnetix.com,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 bsp-development.geo@...ca-geosystems.com
Subject: Re: [PATCH v13 3/3] Input: Add TouchNetix axiom i2c touchscreen driver

Hello Dmitry,

> On Wed, Jun 05, 2024 at 03:48:20PM +0200, Kamel BOUHARA wrote:
>> [...]
>> 
>> > > > +
>> > > > +	error = devm_request_threaded_irq(dev, client->irq, NULL,
>> > > > +					  axiom_irq, IRQF_ONESHOT, dev_name(dev), ts);
>> > > > +	if (error) {
>> > > > +		dev_info(dev, "Request irq failed, falling back to polling mode");
>> > > 
>> > > I do not think you should fall back to polling mode if you fail to get
>> > > interrupt. If it was not specified (client->irq) then I can see that
>> > > we
>> > > might want to fall back, but if the system configured for using
>> > > interrupt and you can not get it you should bail out.
>> > > 
>> > 
>> > Yes, clear, the polling mode can be decorrelated to the irq not provided
>> > case.
>> 
>> Just to make sure I understood, is this what you propose ?
>> 
>> if (client->irq) {
>>         error = devm_request_threaded_irq(...)
>>         if (error) {
>> 		dev_warn(dev, "failed to request IRQ\n");
>> 		client->irq = 0;
>>          }
>> }
>> 
>> if(!client->irq) {
>>     // setup polling stuff
>>     ...
>> }
>
> No, if you fail to acquire interrupt that was described in ACPI/DT it
> should be treated as an error, like this:
>
> 	if (client->irq) {
> 		error = devm_request_threaded_irq(...)
> 		if (error)
> 			return dev_err_probe(...);
> 	} else {
> 		.. set up polling ..
> 	}
>
> This also makes sure that if interrupt controller is not ready and
> requests probe deferral we will not end up with device in polling
> mode.

In the case of probe deferral, I see the benefit of treating it as an
error. However, in the other case, I find it better to fall back to
polling mode with a big error message than just exiting in error. As a
user, I think we prefer having a degraded feature over not having the
feature at all.

So what about something like:

	if (client->irq) {
		error = devm_request_threaded_irq(...)
		if (error == -EPROBE_DEFER)
			return dev_err_probe(...);
		dev_warn("Big error message");
                client->irq = 0;
	}
	if (!client->irq) {
		.. set up polling ..
	}

Gregory

>
> Thanks.
>
> -- 
> Dmitry