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From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Marc Gonzalez <marc.w.gonzalez@free.fr>
Cc: GPIO <linux-gpio@vger.kernel.org>,
	MSM <linux-arm-msm@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: Re: Using a GPIO as an interrupt line
Date: Tue, 19 Nov 2019 09:57:48 +0000	[thread overview]
Message-ID: <20191119095748.GX25745@shell.armlinux.org.uk> (raw)
In-Reply-To: <f0d383f3-8efa-ae68-62af-68f69cd4143f@free.fr>

On Tue, Nov 19, 2019 at 10:28:15AM +0100, Marc Gonzalez wrote:
> Hello,
> 
> The board I'm working on provides a TCA9539 I/O expander.
> Or, as the datasheet(*) calls it, a "Low Voltage 16-Bit I2C and
> SMBus Low-Power I/O Expander with Interrupt Output, Reset Pin,
> and Configuration Registers"
> 
> (*) http://www.ti.com/lit/ds/symlink/tca9539.pdf
> 
> The binding is documented in Documentation/devicetree/bindings/gpio/gpio-pca953x.txt
> 
> I have some doubts about the interrupt output, described as:
> 
> Optional properties:
>  - interrupts: interrupt specifier for the device's interrupt output.
> 
> In my board's DT, the I/O expander is described as:
> 
> 	exp1: gpio@74 {
> 		compatible = "ti,tca9539";
> 		reg = <0x74>;
> 		gpio-controller;
> 		#gpio-cells = <2>;
> 		reset-gpios = <&tlmm 96 GPIO_ACTIVE_LOW>;
> 		pinctrl-names = "default";
> 		pinctrl-0 = <&top_exp_rst>;
> 		interrupt-parent = <&tlmm>;
> 		interrupts = <42 IRQ_TYPE_LEVEL_HIGH>;

This specifies an interrupt signal, number 42, on the tlmm interrupt
controller. It isn't a GPIO specification. Not every interrupt is a
GPIO, and some SoCs can have dedicated interrupt pins that are
exactly that.

Hence, needlessly limiting an external device to requiring a GPIO for
its interrupt is detrimental.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up

WARNING: multiple messages have this Message-ID (diff)
From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Marc Gonzalez <marc.w.gonzalez@free.fr>
Cc: Marc Zyngier <marc.zyngier@arm.com>,
	GPIO <linux-gpio@vger.kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	MSM <linux-arm-msm@vger.kernel.org>
Subject: Re: Using a GPIO as an interrupt line
Date: Tue, 19 Nov 2019 09:57:48 +0000	[thread overview]
Message-ID: <20191119095748.GX25745@shell.armlinux.org.uk> (raw)
In-Reply-To: <f0d383f3-8efa-ae68-62af-68f69cd4143f@free.fr>

On Tue, Nov 19, 2019 at 10:28:15AM +0100, Marc Gonzalez wrote:
> Hello,
> 
> The board I'm working on provides a TCA9539 I/O expander.
> Or, as the datasheet(*) calls it, a "Low Voltage 16-Bit I2C and
> SMBus Low-Power I/O Expander with Interrupt Output, Reset Pin,
> and Configuration Registers"
> 
> (*) http://www.ti.com/lit/ds/symlink/tca9539.pdf
> 
> The binding is documented in Documentation/devicetree/bindings/gpio/gpio-pca953x.txt
> 
> I have some doubts about the interrupt output, described as:
> 
> Optional properties:
>  - interrupts: interrupt specifier for the device's interrupt output.
> 
> In my board's DT, the I/O expander is described as:
> 
> 	exp1: gpio@74 {
> 		compatible = "ti,tca9539";
> 		reg = <0x74>;
> 		gpio-controller;
> 		#gpio-cells = <2>;
> 		reset-gpios = <&tlmm 96 GPIO_ACTIVE_LOW>;
> 		pinctrl-names = "default";
> 		pinctrl-0 = <&top_exp_rst>;
> 		interrupt-parent = <&tlmm>;
> 		interrupts = <42 IRQ_TYPE_LEVEL_HIGH>;

This specifies an interrupt signal, number 42, on the tlmm interrupt
controller. It isn't a GPIO specification. Not every interrupt is a
GPIO, and some SoCs can have dedicated interrupt pins that are
exactly that.

Hence, needlessly limiting an external device to requiring a GPIO for
its interrupt is detrimental.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up

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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2019-11-19  9:58 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-19  9:28 Using a GPIO as an interrupt line Marc Gonzalez
2019-11-19  9:28 ` Marc Gonzalez
2019-11-19  9:57 ` Russell King - ARM Linux admin [this message]
2019-11-19  9:57   ` Russell King - ARM Linux admin
2019-11-19 10:46   ` Marc Gonzalez
2019-11-19 10:46     ` Marc Gonzalez
2019-11-19 10:56     ` Uwe Kleine-König
2019-11-19 10:56       ` Uwe Kleine-König
2019-11-19 11:00       ` Russell King - ARM Linux admin
2019-11-19 11:00         ` Russell King - ARM Linux admin
2019-11-19 11:03         ` Uwe Kleine-König
2019-11-19 11:03           ` Uwe Kleine-König
2019-11-19 10:58     ` Russell King - ARM Linux admin
2019-11-19 10:58       ` Russell King - ARM Linux admin
2019-11-19 11:46       ` Marc Gonzalez
2019-11-19 11:46         ` Marc Gonzalez
2019-11-19 19:19         ` Bjorn Andersson
2019-11-19 19:19           ` Bjorn Andersson
2019-11-19 19:23           ` Jeffrey Hugo
2019-11-19 19:23             ` Jeffrey Hugo
2019-11-19 19:35             ` Bjorn Andersson
2019-11-19 19:35               ` Bjorn Andersson

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