linux-kernel - Re: [PATCH 1/2] watchdog: bd70528: don't crash if WDG is confiured with BD71828

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Message-ID: <20210107151211.GA13040@roeck-us.net>
Date:   Thu, 7 Jan 2021 07:12:11 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc:     mazziesaccount@...il.com,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-power@...rohmeurope.com, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] watchdog: bd70528: don't crash if WDG is confiured
 with BD71828

On Thu, Jan 07, 2021 at 08:37:03AM +0200, Matti Vaittinen wrote:
> If config for BD70528 watchdog is enabled when BD71828 or BD71815
> are used the RTC module will issue call to BD70528 watchdog with
> NULL data. Ignore this call and don't crash.
> 
> Signed-off-by: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>

I really think this should be handled in the calling code.
Also, I am curious how this is supposed to work.

The code is called with

	ret = bd70528_wdt_set(r->parent, new_state & BD70528_WDT_STATE_BIT,
                              old_state);

from bd70528_set_rtc_based_timers(). That same function subsequently
calls bd70528_set_elapsed_tmr() with the same parameter, and that
parameter is dereferenced in bd70528_set_elapsed_tmr() without checking.

Conceptually, it should not be necessary to determine at compile-time
which of the chips is in the system. It should be posible to compile
a single kernel which supports all chips.

Guenter

> ---
>  drivers/watchdog/bd70528_wdt.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/watchdog/bd70528_wdt.c b/drivers/watchdog/bd70528_wdt.c
> index 0170b37e6674..fde242b8a4a6 100644
> --- a/drivers/watchdog/bd70528_wdt.c
> +++ b/drivers/watchdog/bd70528_wdt.c
> @@ -49,6 +49,21 @@ int bd70528_wdt_set(struct rohm_regmap_dev *data, int enable, int *old_state)
>  	u8 wd_ctrl_arr[3] = { WD_CTRL_MAGIC1, WD_CTRL_MAGIC2, 0 };
>  	u8 *wd_ctrl = &wd_ctrl_arr[2];
>  
> +	/*
> +	 * BD71828 and BD71815 use same RTC driver as BD70528.
> +	 * BD71815 and BD71828 do not need MFD data as they do not share
> +	 * RTC counter with watchdog. The BD70528 watchdog should not be
> +	 * compiled in with BD71815 or BD71828 and the stub implementation
> +	 * for the bd70528_wdt_set should be provided instead.
> +	 *
> +	 * If one compiles this watchdog with BD71828 or BD71815 - the call
> +	 * from RTC may get here and the data pointer is NULL. In that case,
> +	 * warn and go out.
> +	 */
> +	if (!data) {
> +		pr_warn("BD70528_WATCHDOG misconfigured\n");
> +		return 0;
> +	}
>  	ret = regmap_read(bd70528->chip.regmap, BD70528_REG_WDT_CTRL, &tmp);
>  	if (ret)
>  		return ret;
> 
> base-commit: 2c85ebc57b3e1817b6ce1a6b703928e113a90442
> -- 
> 2.25.4
> 
> 
> -- 
> Matti Vaittinen, Linux device drivers
> ROHM Semiconductors, Finland SWDC
> Kiviharjunlenkki 1E
> 90220 OULU
> FINLAND
> 
> ~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
> Simon says - in Latin please.
> ~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
> Thanks to Simon Glass for the translation =]