linux-kernel - Re: [PATCH v1 2/2] arm64: dts: qcom: qcs6490-rb3gen2: Enable CAN bus controller

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Message-ID: <316fa702-6cd8-4842-aecf-c176a5a53e2e@oss.qualcomm.com>
Date: Mon, 19 Jan 2026 10:21:37 +0530
From: Viken Dadhaniya <viken.dadhaniya@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: mkl@...gutronix.de, mani@...nel.org, thomas.kopp@...rochip.com,
        mailhol@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
        conor+dt@...nel.org, andersson@...nel.org, konradybcio@...nel.org,
        linux-can@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        mukesh.savaliya@....qualcomm.com, anup.kulkarni@....qualcomm.com
Subject: Re: [PATCH v1 2/2] arm64: dts: qcom: qcs6490-rb3gen2: Enable CAN bus
 controller



On 1/9/2026 7:35 PM, Dmitry Baryshkov wrote:
> On Fri, Jan 09, 2026 at 06:23:39PM +0530, Viken Dadhaniya wrote:
>>
>>
>> On 1/8/2026 7:33 PM, Dmitry Baryshkov wrote:
>>> On Thu, Jan 08, 2026 at 06:22:00PM +0530, Viken Dadhaniya wrote:
>>>> Enable the MCP2518FD CAN controller on the QCS6490 RB3 Gen2 platform.
>>>> The controller is connected via SPI3 and uses a 40 MHz oscillator.
>>>> A GPIO hog for GPIO0 is included to configure the CAN transceiver in
>>>> Normal mode during boot.
>>>
>>> The main question is: what is so different between RB3 Gen2 and previous
>>> RB boards which also incorporated this CAN controller? Are there any
>>> board differences or is it that nobody tested the CAN beforehand?
>>>
>>
>> The behavior is consistent across platforms, but I do not have details on
>> how other platforms were tested.
>>
>> On the RB3Gen2 board, communication with the PCAN interface requires the
>> CAN transceiver to be in normal mode. Since the GPIO-controller support
>> was recently integrated into the driver, I configured the transceiver using a
>> GPIO hog property. Without this configuration, the transceiver is not set
>> to normal mode, and CAN communication does not work.
> 
> How do we verify the mode on a running system? I have the boards, but I
> don't have anything connected to them over the CAN bus.
> 
> BTW: can you recommend any simple setup to actually test the CAN bus on
> those devices?
> 

I tested the CAN controller using the following commands:

1. Loopback Mode Testing (GPIO hog not required)

ip link set can0 down
ip link set can0 type can bitrate 500000 loopback on
ip link set can0 up
cansend can0 12345678#1122334455667788_B
candump can0

2. Testing with External CAN FD Adapter (PCAN-USB FD)
A GPIO hog was required to configure the transceiver in normal mode.

1. Probed and verified CAN transceiver pins and connected them to the
   PCAN-USB FD hardware.
2. Configured the CAN interface:
	
	ip link set can0 down
	ip link set can0 type can bitrate 500000
	ip link set can0 up

3. Configured the PCAN-USB FD software for 500 kbps arbitration bitrate.

4.Sent a CAN FD frame from Linux
	cansend can0 12345678#1122334455667788_B
	
5. Verified reception in the PCAN software.

6. Transmitted frames from the PCAN software and validated them on Linux
	candump can0