Re: [PATCH v3 4/4] watchdog: qcom: add support to read the restart reason from IMEM

[Guenter Roeck <linux@roeck-us.net>]

On 5/2/25 06:17, Kathiravan Thirumoorthy wrote:
> When the system boots up after a watchdog reset, the EXPIRED_STATUS bit
> in the WDT_STS register is cleared. To identify if the system was
> restarted due to WDT expiry, XBL update the information in the IMEM region.
> Update the driver to read the restart reason from IMEM and populate the
> bootstatus accordingly.
> 
> With the CONFIG_WATCHDOG_SYSFS enabled, user can extract the information
> as below:
> 
> cat /sys/devices/platform/soc@0/f410000.watchdog/watchdog/watchdog0/bootstatus
> 32
> 
> For backward compatibility, keep the EXPIRED_STATUS bit check. Add a new
> function qcom_wdt_get_restart_reason() to read the restart reason from
> IMEM.
> 
> Signed-off-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@oss.qualcomm.com>
> ---
> Changes in v3:
> 	- Split the introduction of device data into separate patch
> 	- s/bootloaders/XBL - for clarity of which bootloader is
> 	  involved
> 	- Mention the sysfs path on to extract this information
> 	- s/compatible/imem_compatible in the device data structure to
> 	  avoid the confusion / better naming
> Changes in v2:
> 	- Use the syscon API to access the IMEM region
> 	- Handle the error cases returned by qcom_wdt_get_restart_reason
> 	- Define device specific data to retrieve the IMEM compatible,
> 	  offset and the value for non secure WDT, which allows to
> 	  extend the support for other SoCs
> ---
>   drivers/watchdog/qcom-wdt.c | 40 ++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index dfaac5995c84c1f377023e6e62770c5548528a4c..f2cb8bfdf53a5090bcfff6ea3a23005b629ef948 100644
> --- a/drivers/watchdog/qcom-wdt.c
> +++ b/drivers/watchdog/qcom-wdt.c
> @@ -7,9 +7,11 @@
>   #include <linux/interrupt.h>
>   #include <linux/io.h>
>   #include <linux/kernel.h>
> +#include <linux/mfd/syscon.h>
>   #include <linux/module.h>
>   #include <linux/of.h>
>   #include <linux/platform_device.h>
> +#include <linux/regmap.h>
>   #include <linux/watchdog.h>
>   
>   enum wdt_reg {
> @@ -42,6 +44,9 @@ struct qcom_wdt_match_data {
>   	const u32 *offset;
>   	bool pretimeout;
>   	u32 max_tick_count;
> +	const char *imem_compatible;
> +	unsigned int restart_reason_offset;
> +	unsigned int non_secure_wdt_val;
>   };
>   
>   struct qcom_wdt {
> @@ -185,6 +190,9 @@ static const struct qcom_wdt_match_data match_data_ipq5424 = {
>   	.offset = reg_offset_data_kpss,
>   	.pretimeout = true,
>   	.max_tick_count = 0xFFFFFU,
> +	.imem_compatible = "qcom,ipq5424-imem",
> +	.restart_reason_offset = 0x7b0,
> +	.non_secure_wdt_val = 0x5,
>   };
>   
>   static const struct qcom_wdt_match_data match_data_kpss = {
> @@ -193,6 +201,29 @@ static const struct qcom_wdt_match_data match_data_kpss = {
>   	.max_tick_count = 0xFFFFFU,
>   };
>   
> +static int  qcom_wdt_get_restart_reason(struct qcom_wdt *wdt,
> +					const struct qcom_wdt_match_data *data)
> +{
> +	struct regmap *imem;
> +	unsigned int val;
> +	int ret;
> +
> +	imem = syscon_regmap_lookup_by_compatible(data->imem_compatible);
> +	if (IS_ERR(imem))
> +		return PTR_ERR(imem);
> +
> +	ret = regmap_read(imem, data->restart_reason_offset, &val);
> +	if (ret) {
> +		dev_err(wdt->wdd.parent, "failed to read the restart reason info\n");
> +		return ret;
> +	}
> +
> +	if (val == data->non_secure_wdt_val)
> +		wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +
> +	return 0;
> +}
> +
>   static int qcom_wdt_probe(struct platform_device *pdev)
>   {
>   	struct device *dev = &pdev->dev;
> @@ -273,8 +304,13 @@ static int qcom_wdt_probe(struct platform_device *pdev)
>   	wdt->wdd.parent = dev;
>   	wdt->layout = data->offset;
>   
> -	if (readl(wdt_addr(wdt, WDT_STS)) & 1)
> -		wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +	ret = qcom_wdt_get_restart_reason(wdt, data);
> +	if (ret == -ENODEV) {
> +		if (readl(wdt_addr(wdt, WDT_STS)) & 1)
> +			wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +	} else if (ret) {
> +		return ret;
> +	}

Seems odd to me that there is now a function qcom_wdt_get_restart_reason()
but it doesn't handle all means to get the restart reason. Maybe I missed it,
but what is the reason for that ? Why not move reading WDT_STS into
qcom_wdt_get_restart_reason() as well ?

Guenter


>   
>   	/*
>   	 * If 'timeout-sec' unspecified in devicetree, assume a 30 second
>