Message-ID: <4826def7-5dcb-4453-ab3b-0d14880dab93@ti.com>
Date: Thu, 17 Jul 2025 12:51:05 -0500
From: Judith Mendez <jm@...com>
To: Andrew Davis <afd@...com>, Guenter Roeck <linux@...ck-us.net>
CC: Wim Van Sebroeck <wim@...ux-watchdog.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>, Tero Kristo <kristo@...nel.org>,
        <linux-watchdog@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] watchdog: rti_wdt: Add reaction control

Hi Andrew,

On 7/17/25 11:44 AM, Andrew Davis wrote:
> On 7/17/25 10:24 AM, Judith Mendez wrote:
>> Hi Guenter,
>>
>> On 7/16/25 1:50 PM, Guenter Roeck wrote:
>>> On 7/10/25 07:08, Judith Mendez wrote:
>>>> Hi Guenter, Andrew,
>>>>
>>>> On 7/7/25 5:55 PM, Guenter Roeck wrote:
>>>>> On Mon, Jul 07, 2025 at 04:49:31PM -0500, Andrew Davis wrote:
>>>>>> On 7/7/25 3:58 PM, Guenter Roeck wrote:
>>>>>>> On Mon, Jul 07, 2025 at 01:00:02PM -0500, Judith Mendez wrote:
>>>>>>>> This allows to configure reaction between NMI and reset for WWD.
>>>>>>>>
>>>>>>>> On K3 SoC's other than AM62L SoC [0], watchdog reset output is 
>>>>>>>> routed
>>>>>>>> to the ESM module which can subsequently route the signal to safety
>>>>>>>> master or SoC reset. On AM62L, the watchdog reset output is routed
>>>>>>>> to the SoC HW reset block. So, add a new compatible for AM62l to 
>>>>>>>> add
>>>>>>>> SoC data and configure reaction to reset instead of NMI.
>>>>>>>>
>>>>>>>> [0] https://www.ti.com/product/AM62L
>>>>>>>> Signed-off-by: Judith Mendez <jm@...com>
>>>>>>>> ---
>>>>>>>>    drivers/watchdog/rti_wdt.c | 32 ++++++++++++++++++++++++++++----
>>>>>>>>    1 file changed, 28 insertions(+), 4 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/watchdog/rti_wdt.c 
>>>>>>>> b/drivers/watchdog/rti_wdt.c
>>>>>>>> index d1f9ce4100a8..c9ee443c70af 100644
>>>>>>>> --- a/drivers/watchdog/rti_wdt.c
>>>>>>>> +++ b/drivers/watchdog/rti_wdt.c
>>>>>>>> @@ -35,7 +35,8 @@
>>>>>>>>    #define RTIWWDRXCTRL    0xa4
>>>>>>>>    #define RTIWWDSIZECTRL    0xa8
>>>>>>>> -#define RTIWWDRX_NMI    0xa
>>>>>>>> +#define RTIWWDRXN_RST    0x5
>>>>>>>> +#define RTIWWDRXN_NMI    0xa
>>>>>>>>    #define RTIWWDSIZE_50P        0x50
>>>>>>>>    #define RTIWWDSIZE_25P        0x500
>>>>>>>> @@ -63,22 +64,29 @@
>>>>>>>>    static int heartbeat;
>>>>>>>> +struct rti_wdt_data {
>>>>>>>> +    bool reset;
>>>>>>>> +};
>>>>>>>> +
>>>>>>>>    /*
>>>>>>>>     * struct to hold data for each WDT device
>>>>>>>>     * @base - base io address of WD device
>>>>>>>>     * @freq - source clock frequency of WDT
>>>>>>>>     * @wdd  - hold watchdog device as is in WDT core
>>>>>>>> + * @data - hold configuration data
>>>>>>>>     */
>>>>>>>>    struct rti_wdt_device {
>>>>>>>>        void __iomem        *base;
>>>>>>>>        unsigned long        freq;
>>>>>>>>        struct watchdog_device    wdd;
>>>>>>>> +    const struct rti_wdt_data *data;
>>>>>>>>    };
>>>>>>>>    static int rti_wdt_start(struct watchdog_device *wdd)
>>>>>>>>    {
>>>>>>>>        u32 timer_margin;
>>>>>>>>        struct rti_wdt_device *wdt = watchdog_get_drvdata(wdd);
>>>>>>>> +    u8 reaction;
>>>>>>>>        int ret;
>>>>>>>>        ret = pm_runtime_resume_and_get(wdd->parent);
>>>>>>>> @@ -101,8 +109,13 @@ static int rti_wdt_start(struct 
>>>>>>>> watchdog_device *wdd)
>>>>>>>>         */
>>>>>>>>        wdd->min_hw_heartbeat_ms = 520 * wdd->timeout + 
>>>>>>>> MAX_HW_ERROR;
>>>>>>>> -    /* Generate NMI when wdt expires */
>>>>>>>> -    writel_relaxed(RTIWWDRX_NMI, wdt->base + RTIWWDRXCTRL);
>>>>>>>> +    /* Reset device if wdt serviced outside of window or 
>>>>>>>> generate NMI if available */
>>>>>>>
>>>>>>> Shouldn't that be "or generate NMI if _not_ available" ?
>>>>>>>
>>>>>>
>>>>>> For almost all the K3 devices, the WDT has two selectable outputs, 
>>>>>> one resets
>>>>>> the device directly, the other is this "NMI" which is wired to an 
>>>>>> ESM module
>>>>>> which can take other actions (but usually it just also resets the 
>>>>>> device).
>>>>>> For AM62L that second NMI output is not wired (no ESM module), so 
>>>>>> our only
>>>>>> choice is to set the WDT to direct reset mode.
>>>>>>
>>>>>> The wording is a little strange, but the "or generate NMI if 
>>>>>> available" meaning
>>>>>> if NMI is available, then do that. Reset being the fallback when 
>>>>>> _not_ available.
>>>>>>
>>>>>> Maybe this would work better:
>>>>>>
>>>>>> /* If WDT is serviced outside of window, generate NMI if 
>>>>>> available, or reset device */
>>>>>>
>>>>>
>>>>> The problem is that the code doesn't match the comment. The code 
>>>>> checks the
>>>>> "reset" flag and requests a reset if available. If doesn't check an 
>>>>> "nmi"
>>>>> flag.
>>>>>
>>>>> If the preference is NMI, as your comment suggests, the flag should 
>>>>> be named
>>>>> "nmi" and be set if NMI is available. That would align the code and 
>>>>> the
>>>>> comment. Right now both code and comment are misleading, since the 
>>>>> presence
>>>>> of a reset flag (and setting it to false) suggests that a direct 
>>>>> reset is
>>>>> not available, and that reset is preferred if available. A reset is 
>>>>> the
>>>>> normally expected behavior for a watchdog, so the fact that this is 
>>>>> _not_
>>>>> the case for this watchdog should be made more visible.
>>>>
>>>>
>>>> How about:
>>>>
>>>>
>>>> /* If WWDT serviced outside of window, generate NMI or reset the device
>>>> if NMI not available */
>>>>
>>>> if (wdt->data->reset)
>>>>      reaction = RTIWWDRXN_RST;
>>>> else
>>>>      reaction = RTIWWDRXN_NMI;
>>>>
>>>
>>> As I have said before, the problem is the "reset" flag. Its name 
>>> suggests that
>>> it means "reset is available". That is not what it actually means. It 
>>> means
>>> "NMI is not available". So I suggested to rename it to "nmi" or maybe 
>>> "no_nmi".
>>> Please educate me - why is that such a problem to name the flag to 
>>> match its
>>> meaning ?
>>
>> wdt->data->reset makes more sense because it shows there is a
>> physical line routed to the MAIN RESET HW LOGIC:
>>
>>  >> if (wdt->data->reset)
>>  >>      reaction = RTIWWDRXN_RST;
>>  >> else
>>  >>      reaction = RTIWWDRXN_NMI;
>>
>> If there is a direct reset line to MAIN RESET HW logic, then the
>> reaction should be reset, if there is no reset line, then generate
>> and NMI to ESM.
>>
> 
> There is a reset line on all K3 devices, if you did it this way then
> all devices would have wdt->data->reset set to true and you wouldn't
> need this logic at all. The thing that changes is if NMI/ESM is
> available or not, so as Guenter suggests the flag should be called
> "nmi" or similar and you switch on that.

Looking at the integration spec, I do not see a direct reset line for
any device besides am62l, could you confirm that what I am reading
is correct please?

  ~ Judith

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