Re: [PATCH v2] watchdog: meson: keep running if already active

From: Philippe Boos <pboos@baylibre.com>
To: Guenter Roeck <linux@roeck-us.net>,
	Wim Van Sebroeck <wim@linux-watchdog.org>,
	Neil Armstrong <narmstrong@baylibre.com>
Cc: Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
	"open list:WATCHDOG DEVICE DRIVERS"
	<linux-watchdog@vger.kernel.org>,
	"moderated list:ARM/Amlogic Meson SoC support" 
	<linux-arm-kernel@lists.infradead.org>,
	"open list:ARM/Amlogic Meson SoC support" 
	<linux-amlogic@lists.infradead.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] watchdog: meson: keep running if already active
Date: Thu, 11 Aug 2022 16:03:53 +0200	[thread overview]
Message-ID: <51d8767e-f73c-6045-871f-88b4df098cb2@baylibre.com> (raw)
In-Reply-To: <7ab495dd-4b3e-46e8-6db0-1dd20860043f@roeck-us.net>

On 8/8/22 13:58, Guenter Roeck wrote:
> On 8/1/22 02:21, Philippe Boos wrote:
>> If the watchdog is already running (e.g.: started by bootloader) then
>> the kernel driver should keep the watchdog active but the amlogic driver
>> turns it off.
>>
>> Let the driver fix the clock rate if already active because we do not
>> know the previous timebase value. To avoid unintentional resetting we
>> temporarily set it to its maximum value.
>>
>> Then keep the enable bit if is was previously active.
>>
>> Signed-off-by: Philippe Boos <pboos@baylibre.com>
> 
> What changed since v1 ?
In v1, we read watchdog's enable bit before writing its config register,
then we write the register, this will always stop the watchdog. If it
was previously active we restart it. So, in v1, if the kernel crashes
just before the watchdog restarts it will be stuck forever.

In v2, we read watchdog's enable bit before writing its config register,
if it is already active we keep the enable bit when writing the
register.

Regards,

Philippe Boos
> 
> Guenter
> 
>> ---
>>   drivers/watchdog/meson_gxbb_wdt.c | 24 +++++++++++++++++++-----
>>   1 file changed, 19 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/watchdog/meson_gxbb_wdt.c b/drivers/watchdog/meson_gxbb_wdt.c
>> index 5a9ca10fbcfa..8be8fd9e5637 100644
>> --- a/drivers/watchdog/meson_gxbb_wdt.c
>> +++ b/drivers/watchdog/meson_gxbb_wdt.c
>> @@ -146,6 +146,7 @@ static int meson_gxbb_wdt_probe(struct platform_device *pdev)
>>       struct device *dev = &pdev->dev;
>>       struct meson_gxbb_wdt *data;
>>       int ret;
>> +    u32 ctrl_reg;
>>         data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
>>       if (!data)
>> @@ -177,13 +178,26 @@ static int meson_gxbb_wdt_probe(struct platform_device *pdev)
>>       data->wdt_dev.timeout = DEFAULT_TIMEOUT;
>>       watchdog_set_drvdata(&data->wdt_dev, data);
>>   +    ctrl_reg = readl(data->reg_base + GXBB_WDT_CTRL_REG) &
>> +                GXBB_WDT_CTRL_EN;
>> +
>> +    if (ctrl_reg) {
>> +        /* Watchdog is running - keep it running but extend timeout
>> +         * to the maximum while setting the timebase
>> +         */
>> +        set_bit(WDOG_HW_RUNNING, &data->wdt_dev.status);
>> +        meson_gxbb_wdt_set_timeout(&data->wdt_dev,
>> +                GXBB_WDT_TCNT_SETUP_MASK / 1000);
>> +    }
>> +
>>       /* Setup with 1ms timebase */
>> -    writel(((clk_get_rate(data->clk) / 1000) & GXBB_WDT_CTRL_DIV_MASK) |
>> -        GXBB_WDT_CTRL_EE_RESET |
>> -        GXBB_WDT_CTRL_CLK_EN |
>> -        GXBB_WDT_CTRL_CLKDIV_EN,
>> -        data->reg_base + GXBB_WDT_CTRL_REG);
>> +    ctrl_reg |= ((clk_get_rate(data->clk) / 1000) &
>> +            GXBB_WDT_CTRL_DIV_MASK) |
>> +            GXBB_WDT_CTRL_EE_RESET |
>> +            GXBB_WDT_CTRL_CLK_EN |
>> +            GXBB_WDT_CTRL_CLKDIV_EN;
>>   +    writel(ctrl_reg, data->reg_base + GXBB_WDT_CTRL_REG);
>>       meson_gxbb_wdt_set_timeout(&data->wdt_dev, data->wdt_dev.timeout);
>>         watchdog_stop_on_reboot(&data->wdt_dev);
> 