Message-ID: <92be34eb-2408-4273-9e37-bec0b0d68f10@ti.com>
Date: Thu, 17 Jul 2025 11:44:42 -0500
From: Andrew Davis <afd@...com>
To: Judith Mendez <jm@...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

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.

Andrew

> then the comment could be simplified to:
> 
> /* If WWDT serviced outside of window, generate reset or NMI to ESM */
> 
> to match the code better if you like.
> 
> ~ Judith
> 
> 
> 

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