RZ-G/debug tricks

This page contains many helpful suggestions for debugging issue with the Linux kernel.

Common Tools

• grep : The kernel has thousands of files. The grep tool is the most powerful way to find what you are looking for. Use the -R to search recursively . Remember that grep is case sensitive by default, so use -i if you need it to ignore case.
  • And example to find a function name start_kernel: $ grep -r "start_kernel"
• find : Sometimes someone will give you just a filename, and the find command can help you find where that file is. Also, it find is very helpful when combined with grep.
  • For example, if you just want to search header files: $ find * -name "*.h" | grep purple

Error Messages

• Many times an error message will be printed out. This happens a lot for a device driver that has trouble initializing during boot.
• Your first step should be to find what source code file is print that message
• Simply use the grep command with -R option and search for that error message.

Error Codes

• If a error message prints out an error code, for example "-110", you should look up what the error code means.
• You can find a list of the error code numbers mean in file include/uapi/asm-generic/errno-base.h
• Since the code will use the #defrine name (not the actual number), you can then search driver file for when that error code/name is returned.

Finding the Device Driver File

• When adding or configuring a driver to your system, you will probably be editing the Device Tree.
• If there is an issue with that driver or peripheral, you will need to find the source code for the driver
• You can use the "compatible" name listed in the device tree, and grep, in order to find the location of the device driver file.
• Do you search starting in the "drivers" directory (to avoid all the matches that will be found in other device tree files)
• Example: Find the Watchdog Timer Driver
  • RZ/G2L Device Tree: rz_linux-cip/arch/arm64/boot/dts/renesas/r9a07g044.dtsi

    wdt0: watchdog@12800800 {
    	compatible = "renesas,r9a07g044-wdt",
    		     "renesas,rzg2l-wdt";
    	reg = <0 0x12800800 0 0x400>;
    	clocks = <&cpg CPG_MOD R9A07G044_WDT0_PCLK>,
    		 <&cpg CPG_MOD R9A07G044_WDT0_CLK>;
    	clock-names = "pclk", "oscclk";
    	interrupts = <GIC_SPI 49 IRQ_TYPE_LEVEL_HIGH>,
    		     <GIC_SPI 50 IRQ_TYPE_LEVEL_HIGH>;
    	interrupt-names = "wdt", "perrout";
    	resets = <&cpg R9A07G044_WDT0_PRESETN>;
    	power-domains = <&cpg>;
    	status = "disabled";
    };
    

  • Use the grep command:

    $ grep -R "renesas,rzg2l-wdt" *
    arch/arm64/boot/dts/renesas/r9a07g044.dtsi:				     "renesas,rzg2l-wdt";
    arch/arm64/boot/dts/renesas/r9a07g044.dtsi:				     "renesas,rzg2l-wdt";
    arch/arm64/boot/dts/renesas/r9a07g044.dtsi:				     "renesas,rzg2l-wdt";
    arch/arm64/boot/dts/renesas/r9a07g043.dtsi:				     "renesas,rzg2l-wdt";
    arch/arm64/boot/dts/renesas/r9a07g043.dtsi:				     "renesas,rzg2l-wdt";
    arch/arm64/boot/dts/renesas/r9a07g054.dtsi:				     "renesas,rzg2l-wdt";
    arch/arm64/boot/dts/renesas/r9a07g054.dtsi:				     "renesas,rzg2l-wdt";
    arch/arm64/boot/dts/renesas/r9a07g054.dtsi:				     "renesas,rzg2l-wdt";
    Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml:          - const: renesas,rzg2l-wdt     # RZ/G2L
    Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml:              - renesas,rzg2l-wdt
    drivers/watchdog/rzg2l_wdt.c:	{ .compatible = "renesas,rzg2l-wdt", },
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g044.dtsi:				     "renesas,rzg2l-wdt";
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g044.dtsi:				     "renesas,rzg2l-wdt";
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g044.dtsi:				     "renesas,rzg2l-wdt";
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g043.dtsi:				     "renesas,rzg2l-wdt";
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g043.dtsi:				     "renesas,rzg2l-wdt";
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g054.dtsi:				     "renesas,rzg2l-wdt";
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g054.dtsi:				     "renesas,rzg2l-wdt";
    scripts/dtc/include-prefixes/arm64/renesas/r9a07g054.dtsi:				     "renesas,rzg2l-wdt";
    

  • The very bottom of file drivers/watchdog/rzg2l_wdt.c

    static const struct of_device_id rzg2l_wdt_ids[] = {
    	{ .compatible = "renesas,rzg2l-wdt", },
    	{ /* sentinel */ }
    };
    MODULE_DEVICE_TABLE(of, rzg2l_wdt_ids);
    
    static struct platform_driver rzg2l_wdt_driver = {
    	.driver = {
    		.name = "rzg2l_wdt",
    		.of_match_table = rzg2l_wdt_ids,
    	},
    	.probe = rzg2l_wdt_probe,
    };
    module_platform_driver(rzg2l_wdt_driver);
    
    MODULE_DESCRIPTION("Renesas RZ/G2L WDT Watchdog Driver");
    MODULE_AUTHOR("Biju Das ");
    MODULE_LICENSE("GPL v2");