[PATCH v2] arm64: dts: qcom: Enable CAN RX via GPIO expander

[PATCH v2] arm64: dts: qcom: Enable CAN RX via GPIO expander

[Anup Kulkarni]

Few CAN controllers, part of RTSS sub-system on LeMans, route
their RX signal through a I2C GPIO expander at address 0x3b.
RTSS subsystem is an MCU like sub-system on LeMans with independent
booting capability through OSPI interface and supports peripherals
like RGMII, CAN-FD, UART, I2C, SPI etc.

Describe LeMans EVK hardware  wiring by configuring the
expander GPIO 4 pin as hog with output-high, asserting the selected
line during boot.

Signed-off-by: Anup Kulkarni <anup.kulkarni@oss.qualcomm.com>
---
v1->v2
- Fixed commit text to include platform name.
---
 arch/arm64/boot/dts/qcom/lemans-evk.dts | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/lemans-evk.dts b/arch/arm64/boot/dts/qcom/lemans-evk.dts
index c665db6a4595..34dfc8d22b6a 100644
--- a/arch/arm64/boot/dts/qcom/lemans-evk.dts
+++ b/arch/arm64/boot/dts/qcom/lemans-evk.dts
@@ -616,6 +616,13 @@ expander3: gpio@3b {
 		interrupts-extended = <&tlmm 39 IRQ_TYPE_LEVEL_LOW>;
 		pinctrl-0 = <&expander3_int>;
 		pinctrl-names = "default";
+
+		rtss-can-sel-hog {
+			gpio-hog;
+			gpios = <4 GPIO_ACTIVE_HIGH>;
+			output-high;
+			line-name = "rtss-can-sel";
+		};
 	};
 
 	eeprom@50 {
-- 
2.34.1

Re: [PATCH v2] arm64: dts: qcom: Enable CAN RX via GPIO expander

[Bjorn Andersson]

On Thu, May 07, 2026 at 05:23:24PM +0530, Anup Kulkarni wrote:

The subject prefix is there to quickly inform the reader of "git log
--oneline" what area is being changed. Add "lemans-evk" to match other
changes in this file.

> Few CAN controllers, part of RTSS sub-system on LeMans, route
> their RX signal through a I2C GPIO expander at address 0x3b.

If only a few of them route their RX signal through some I2C GPIO
expander, what are the other ones doing? And how does this relate to a
gpio hog?

> RTSS subsystem is an MCU like sub-system on LeMans with independent
> booting capability through OSPI interface and supports peripherals
> like RGMII, CAN-FD, UART, I2C, SPI etc.
> 

https://docs.kernel.org/process/submitting-patches.html#describe-your-changes
has the following statement in the first paragraph:
"Convince the reviewer that there is a problem worth fixing and that it
makes sense for them to read past the first paragraph."

> Describe LeMans EVK hardware  wiring by configuring the

Double space...

> expander GPIO 4 pin as hog with output-high,

You're not describing the wiring, you're hogging a GPIO to be high.

> asserting the selected line during boot.

But does that GPIO relate to RTSS, the CAN controller, the RX signal,
some form of chip select? Why should this pin be high?

Regards,
Bjorn

> 
> Signed-off-by: Anup Kulkarni <anup.kulkarni@oss.qualcomm.com>
> ---
> v1->v2
> - Fixed commit text to include platform name.
> ---
>  arch/arm64/boot/dts/qcom/lemans-evk.dts | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/lemans-evk.dts b/arch/arm64/boot/dts/qcom/lemans-evk.dts
> index c665db6a4595..34dfc8d22b6a 100644
> --- a/arch/arm64/boot/dts/qcom/lemans-evk.dts
> +++ b/arch/arm64/boot/dts/qcom/lemans-evk.dts
> @@ -616,6 +616,13 @@ expander3: gpio@3b {
>  		interrupts-extended = <&tlmm 39 IRQ_TYPE_LEVEL_LOW>;
>  		pinctrl-0 = <&expander3_int>;
>  		pinctrl-names = "default";
> +
> +		rtss-can-sel-hog {
> +			gpio-hog;
> +			gpios = <4 GPIO_ACTIVE_HIGH>;
> +			output-high;
> +			line-name = "rtss-can-sel";
> +		};
>  	};
>  
>  	eeprom@50 {
> -- 
> 2.34.1
>