Re: [PATCH v8 4/5] watchdog: qcom: add support to get the bootstatus from IMEM

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

On 2/26/26 08:59, 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_bootstatus() to read the restart reason from
> IMEM.
> 
> Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> Signed-off-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@oss.qualcomm.com>
> ---
> Changes in v8:
> 	- Picked up the R-b tag
> 	- Updated the comment as suggested by Konrad
> Changes in v7:
> 	- no changes
> Changes in v6:
> 	- Reworked to get the restart reason code from SRAM region
> 
> Changes in v5:
> 	- Use dev_err_probe instead of dev_err
> 
> Changes in v4:
> 	- Kept only WDIOF_CARDRESET and dropped other codes
> 	- Renamed qcom_wdt_get_reason_reason() to
> 	  qcom_wdt_get_bootstatus()
> 	- Moved the existing check inside qcom_wdt_get_bootstatus()
> 	- Dropped the device data and put all the details in the DT node
> 
> 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 | 42 ++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index dfaac5995c84c1f377023e6e62770c5548528a4c..bbf229a7b5840714b9429f4b092ec3f7a6a26961 100644
> --- a/drivers/watchdog/qcom-wdt.c
> +++ b/drivers/watchdog/qcom-wdt.c
> @@ -9,6 +9,7 @@
>   #include <linux/kernel.h>
>   #include <linux/module.h>
>   #include <linux/of.h>
> +#include <linux/of_address.h>
>   #include <linux/platform_device.h>
>   #include <linux/watchdog.h>
>   
> @@ -42,6 +43,7 @@ struct qcom_wdt_match_data {
>   	const u32 *offset;
>   	bool pretimeout;
>   	u32 max_tick_count;
> +	u32 wdt_reason_val;
>   };
>   
>   struct qcom_wdt {
> @@ -185,6 +187,7 @@ static const struct qcom_wdt_match_data match_data_ipq5424 = {
>   	.offset = reg_offset_data_kpss,
>   	.pretimeout = true,
>   	.max_tick_count = 0xFFFFFU,
> +	.wdt_reason_val = 5,
>   };
>   
>   static const struct qcom_wdt_match_data match_data_kpss = {
> @@ -193,6 +196,40 @@ static const struct qcom_wdt_match_data match_data_kpss = {
>   	.max_tick_count = 0xFFFFFU,
>   };
>   
> +static int qcom_wdt_get_bootstatus(struct device *dev, struct qcom_wdt *wdt,
> +				   u32 val)
> +{
> +	struct device_node *imem;
> +	struct resource res;
> +	void __iomem *addr;
> +	int ret;
> +
> +	imem = of_parse_phandle(dev->of_node, "sram", 0);
> +	if (!imem) {
> +		/* Read the EXPIRED_STATUS bit as a fallback */
> +		if (readl(wdt_addr(wdt, WDT_STS)) & 1)
> +			wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +
> +		return 0;
> +	}
> +
> +	ret = of_address_to_resource(imem, 0, &res);
> +	of_node_put(imem);
> +	if (ret)
> +		return ret;
> +
> +	addr = ioremap(res.start, resource_size(&res));
> +	if (!addr)
> +		return -ENOMEM;
> +
> +	if (readl(addr) == val)
> +		wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +
> +	iounmap(addr);
> +
> +	return 0;
> +}
> +
>   static int qcom_wdt_probe(struct platform_device *pdev)
>   {
>   	struct device *dev = &pdev->dev;
> @@ -273,8 +310,9 @@ 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_bootstatus(dev, wdt, data->wdt_reason_val);
> +	if (ret)
> +		return ret;
>   

Why is reporting the boot status so important that the failure to read it
results in refusing to instantiate the driver ? That warrants a detailed
explanation, even more so since it is not backward compatible.

Guenter

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