Re: [PATCH v1] arm64: dts: qcom: Enable CAN RX via GPIO expander

[Anup Kulkarni <anup.kulkarni@oss.qualcomm.com>]

On 4/14/2026 11:39 PM, Dmitry Baryshkov wrote:
> On Tue, Apr 14, 2026 at 06:20:14PM +0200, Konrad Dybcio wrote:
>> On 4/14/26 6:08 PM, Dmitry Baryshkov wrote:
>>> On Thu, Apr 02, 2026 at 04:22:53PM +0530, Anup Kulkarni wrote:
>>>> 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 this hardware wiring by configuring the expander GPIO 4 pin as
>>>> hog with output-high, asserting the selected line during boot.
>>> Missing platform name in the subject.
Will update the name in the next patch.
>>>
>>>> Signed-off-by: Anup Kulkarni <anup.kulkarni@oss.qualcomm.com>
>>>> ---
>>>>  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 a1ef4eba2a20..b8371bdf9933 100644
>>>> --- a/arch/arm64/boot/dts/qcom/lemans-evk.dts
>>>> +++ b/arch/arm64/boot/dts/qcom/lemans-evk.dts
>>>> @@ -615,6 +615,13 @@ expander3: gpio@3b {
>>>>  		interrupts-extended = <&tlmm 39 IRQ_TYPE_LEVEL_LOW>;
>>>>  		pinctrl-0 = <&expander3_int>;
>>>>  		pinctrl-names = "default";
>>>> +
>>>> +		rtss-can-sel-hog {
>>> Why is it being described as a hog rather than a pinctrl used by the
>>> CAN device?

The RTSS CAN device is active at boot-up so used hog property here. 

>> My understanding is that the CAN bus is managed by SAIL ("RTSS")
> So, Linux can affect what is being required for the safety island?

Yes, CAN bus is managed by RTSS, but the transceivers are

outside of RTSS. The RX line of CAN device is connected to the transceiver through I2C

GPIO expander on board level. GPIO Expander pin enables mux to connect CAN RX to transceiver. 

>