linux-kernel - Re: [PATCH v2 5/5] watchdog: qcom: add support to read the restart reason from IMEM

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Message-ID: <4e9621c2-f347-4cba-9422-b14f96ee4c0b@oss.qualcomm.com>
Date: Wed, 16 Apr 2025 16:51:48 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck
 <linux@...ck-us.net>,
        Rajendra Nayak <quic_rjendra@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v2 5/5] watchdog: qcom: add support to read the restart
 reason from IMEM

On 4/16/25 10:29 AM, 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, bootloaders update the information in the IMEM region.
> Update the driver to read the restart reason from IMEM and populate the
> bootstatus accordingly.
> 
> 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@....qualcomm.com>
> ---
> 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 | 47 +++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 45 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index 006f9c61aa64fd2b4ee9db493aeb54c8fafac818..94ba9ec9907a19854cd45a94f8da17d6e6eb33bc 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 {
> @@ -39,6 +41,9 @@ static const u32 reg_offset_data_kpss[] = {
>  };
>  
>  struct qcom_wdt_match_data {
> +	const char *compatible;
> +	unsigned int restart_reason_offset;
> +	unsigned int non_secure_wdt_val;
>  	const u32 *offset;
>  	bool pretimeout;
>  	u32 max_tick_count;
> @@ -175,6 +180,15 @@ static const struct watchdog_info qcom_wdt_pt_info = {
>  	.identity	= KBUILD_MODNAME,
>  };
>  
> +static const struct qcom_wdt_match_data match_data_ipq5424 = {
> +	.compatible = "qcom,ipq5424-imem",
> +	.restart_reason_offset = 0x7b0,
> +	.non_secure_wdt_val = 0x5,
> +	.offset = reg_offset_data_kpss,
> +	.pretimeout = true,
> +	.max_tick_count = 0xFFFFFU,
> +};
> +
>  static const struct qcom_wdt_match_data match_data_apcs_tmr = {
>  	.offset = reg_offset_data_apcs_tmr,
>  	.pretimeout = false,
> @@ -187,6 +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,

double space> +					const struct qcom_wdt_match_data *data)

Please align this

> +{
> +	struct regmap *imem;
> +	unsigned int val;
> +	int ret;
> +
> +	imem = syscon_regmap_lookup_by_compatible(data->compatible);

I still think nvmem could be better here, as it allows to plug in
more magic values

Konrad