linux-kernel - Re: Input: ep93xx_keypad: Checking for a failed platform_get_irq() call in ep93xx_keypad

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Message-ID: <20200409204819.GR75430@dtor-ws>
Date:   Thu, 9 Apr 2020 13:48:19 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Markus Elfring <Markus.Elfring@....de>
Cc:     linux-input@...r.kernel.org, Allison Randal <allison@...utok.net>,
        Arnd Bergmann <arnd@...db.de>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>,
        Olof Johansson <olof@...om.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Tang Bin <tangbin@...s.chinamobile.com>
Subject: Re: Input: ep93xx_keypad: Checking for a failed platform_get_irq()
 call in ep93xx_keypad_probe()

Hi Markus,

On Wed, Apr 08, 2020 at 06:52:31PM +0200, Markus Elfring wrote:
> Hello,
> 
> I have taken another look at the implementation of the function “ep93xx_keypad_probe”.
> A software analysis approach points the following source code out for
> further development considerations.
> https://elixir.bootlin.com/linux/v5.6.3/source/drivers/input/keyboard/ep93xx_keypad.c#L252
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/input/keyboard/ep93xx_keypad.c?id=f5e94d10e4c468357019e5c28d48499f677b284f#n252
> 
>  	keypad->irq = platform_get_irq(pdev, 0);
>  	if (!keypad->irq) {
>  		err = -ENXIO;
>  		goto failed_free;
>  	}
> 
> 
> The software documentation is providing the following information
> for the used programming interface.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/base/platform.c?id=f5e94d10e4c468357019e5c28d48499f677b284f#n221
> https://elixir.bootlin.com/linux/v5.6.3/source/drivers/base/platform.c#L202
> 
> “…
>  * Return: IRQ number on success, negative error number on failure.
> …”
> 
> Would you like to reconsider the shown condition check?

Platform code historically allowed creating IRQ resources with IRQ
number 0 to indicate "no interrupt assigned", so this driver tries to
filter out such conditions. The negative IRQs (errors) will be rejected
by request_irq() but I guess we can lose -EPROBE_DEFER. We could do

	if (keypad->irq <= 0) {
		err = keypad->irq ?: -ENXIO : keypad->irq;
		goto failed_free;
	}


or, maybe we should take a look at platform_get_irq() and see if we can
stop it returning 0 interrupt numbers and clean up the drivers.

Thanks.

-- 
Dmitry