Re: [PATCH v2 3/3] watchdog:rit_wdt: Add support for WDIOF_CARDRESET

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

On 7/11/23 02:17, huaqian.li@siemens.com wrote:
> From: Li Hua Qian <huaqian.li@siemens.com>
> 
> This patch adds the WDIOF_CARDRESET support for the platform watchdog
> whose hardware does not support this feature, to know if the board
> reboot is due to a watchdog reset.
> 
> This is done via reserved memory(RAM), which indicates if specific
> info saved, triggering the watchdog reset in last boot.
> 
> Signed-off-by: Li Hua Qian <huaqian.li@siemens.com>
> ---
>   drivers/watchdog/rti_wdt.c | 48 ++++++++++++++++++++++++++++++++++++++
>   1 file changed, 48 insertions(+)
> 
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index ce8f18e93aa9..77fd6b54137c 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -18,6 +18,7 @@
>   #include <linux/pm_runtime.h>
>   #include <linux/types.h>
>   #include <linux/watchdog.h>
> +#include <linux/of.h>
>   
>   #define DEFAULT_HEARTBEAT 60
>   
> @@ -52,6 +53,11 @@
>   
>   #define DWDST			BIT(1)
>   
> +#define PON_REASON_SOF_NUM	0xBBBBCCCC
> +#define PON_REASON_MAGIC_NUM	0xDDDDDDDD
> +#define PON_REASON_EOF_NUM	0xCCCCBBBB
> +#define PON_REASON_ITEM_BITS	0xFFFFFFFF
> +
>   static int heartbeat = DEFAULT_HEARTBEAT;
>   
>   /*
> @@ -198,6 +204,11 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   	struct rti_wdt_device *wdt;
>   	struct clk *clk;
>   	u32 last_ping = 0;
> +	u32 reserved_mem_size;
> +	unsigned long *vaddr;
> +	unsigned long paddr;
> +	u32 data[3];
> +	u32 reg[8];
>   
>   	wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
>   	if (!wdt)
> @@ -284,6 +295,43 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   		}
>   	}
>   
> +	ret = of_property_read_variable_u32_array(pdev->dev.of_node, "reg", reg,
> +					 0, ARRAY_SIZE(reg));
> +	if (ret < 0) {
> +		dev_err(dev, "cannot read the reg info.\n");
> +		goto err_iomap;
> +	}

This aborts if the property does not exist, which is unacceptable.
Any such addition must be optional.

> +
> +	/*
> +	 * If reserved memory is defined for watchdog reset cause.
> +	 * Readout the Power-on(PON) reason and pass to bootstatus.
> +	 */
> +	if (ret == 8) {
> +		paddr = reg[5];
> +		reserved_mem_size = reg[7];

It seems odd that reserved_mem_size is not checked, and that it is even provided
given that it needs to be (at least) 24 bytes, and any other value does not really
make sense.

> +		vaddr = memremap(paddr, reserved_mem_size, MEMREMAP_WB);
> +		if (vaddr == NULL) {
> +			dev_err(dev, "Failed to map memory-region.\n");
> +			goto err_iomap;

This returns 8, which would be an odd error return.

> +		}
> +
> +		data[0] = *vaddr & PON_REASON_ITEM_BITS;
> +		data[1] = *(vaddr + 1) & PON_REASON_ITEM_BITS;
> +		data[2] = *(vaddr + 2) & PON_REASON_ITEM_BITS;
> +

The & seems pointless / wasteful. Why ignore the upper 32 bits of each location ?
Either make it u32 or make it u64 and use the entire 64 bit. Besides,
vaddr[0..2] would make the code much easier to read.

> +		dev_dbg(dev, "Watchdog: sof = %lX, data = %lX, eof = %lX\n",
> +			data[0], data[1], data[2]);
> +
> +		if ((data[0] == PON_REASON_SOF_NUM)
> +		    && (data[1] == PON_REASON_MAGIC_NUM)
> +		    && (data[1] == PON_REASON_MAGIC_NUM)) {

Unnecessary inner (), and I don't see the point of checking data[1] twice.

> +			dev_info(dev, "Watchdog reset cause detected.\n");

Unnecessary noise.

> +			wdd->bootstatus |= WDIOF_CARDRESET;
> +		}
> +		memset(vaddr, 0, reserved_mem_size);
> +		memunmap(vaddr);
> +	}

And some random data in the property is acceptable ? That is odd, especially
after mandating the property itself.

> +
>   	watchdog_init_timeout(wdd, heartbeat, dev);
>   
>   	ret = watchdog_register_device(wdd);