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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 2/27/26 8:42 AM, Guenter Roeck wrote:
> 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.

This only fails if the reference passed in the new 'sram' property is present,
but invalid

Konrad