[PATCH v4 15/19] watchdog: s3c2410_wdt: Add support for WTCON register DBGACK_MASK bit

[Guenter Roeck]

On 11/20/23 14:45, Peter Griffin wrote:
> Hi Guenter,
> 
> Thanks for the review.
> 
> On Mon, 20 Nov 2023 at 22:00, Guenter Roeck <linux at roeck-us.net> wrote:
>>
>> On 11/20/23 13:20, Peter Griffin wrote:
>>> The WDT uses the CPU core signal DBGACK to determine whether the SoC
>>> is running in debug mode or not. If the DBGACK signal is asserted and
>>> DBGACK_MASK is enabled, then WDT output and interrupt is masked.
>>>
>>> Presence of the DBGACK_MASK bit is determined by adding a new
>>> QUIRK_HAS_DBGACK_BIT quirk. Currently only gs101 SoC is known to have
>>> the DBGACK_MASK bit so add the quirk to drv_data_gs101_cl1 and
>>> drv_data_gs101_cl1 quirks.
>>>
>>> Signed-off-by: Peter Griffin <peter.griffin at linaro.org>
>>> ---
>>>    drivers/watchdog/s3c2410_wdt.c | 32 +++++++++++++++++++++++++++-----
>>>    1 file changed, 27 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
>>> index 08b8c57dd812..ed561deeeed9 100644
>>> --- a/drivers/watchdog/s3c2410_wdt.c
>>> +++ b/drivers/watchdog/s3c2410_wdt.c
>>> @@ -34,9 +34,10 @@
>>>
>>>    #define S3C2410_WTCNT_MAXCNT        0xffff
>>>
>>> -#define S3C2410_WTCON_RSTEN  (1 << 0)
>>> -#define S3C2410_WTCON_INTEN  (1 << 2)
>>> -#define S3C2410_WTCON_ENABLE (1 << 5)
>>> +#define S3C2410_WTCON_RSTEN          (1 << 0)
>>> +#define S3C2410_WTCON_INTEN          (1 << 2)
>>> +#define S3C2410_WTCON_ENABLE         (1 << 5)
>>> +#define S3C2410_WTCON_DBGACK_MASK    (1 << 16)
>>>
>>>    #define S3C2410_WTCON_DIV16 (0 << 3)
>>>    #define S3C2410_WTCON_DIV32 (1 << 3)
>>> @@ -107,12 +108,16 @@
>>>     * %QUIRK_HAS_PMU_CNT_EN: PMU block has some register (e.g. CLUSTERx_NONCPU_OUT)
>>>     * with "watchdog counter enable" bit. That bit should be set to make watchdog
>>>     * counter running.
>>> + *
>>> + * %QUIRK_HAS_DBGACK_BIT: WTCON register has DBGACK_MASK bit. Enables masking
>>> + * WDT interrupt and reset request according to CPU core DBGACK signal.
>>
>> This is a bit difficult to understand. I _think_ it means that the DBGACK_MASK bit
>> has to be set to be able to trigger interrupt and reset requests.
> 
> Not quite, it is a bit that controls masking the watchdog outputs when the SoC
> is in debug mode.
> 
>> "masking" normally refers to disabling something (at least in interrupt context).
>> "Enables masking WDT interrupt" sounds like the bit has to be set in order to
>> be able to disable interupts, and the code below suggests that the bit has to be
>> set for the driver to work. Is that the case ? It might make sense to explain this
>> a bit further.
> 
> Maybe I explained it more clearly in the commit message than the comment
> 
> "The WDT uses the CPU core signal DBGACK to determine whether the SoC
> is running in debug mode or not. If the DBGACK signal is asserted and
> DBGACK_MASK is enabled, then WDT output and interrupt is masked."
> 
> Is that any clearer? Or maybe simpler again
> 
> "Enabling DBGACK_MASK bit masks the watchdog outputs when the SoC is
> in debug mode. Debug mode is determined by the DBGACK CPU signal."
> 
> Let me know what you think is the clearest and most succinct and I can
> update the comment.
> 

You are still using the term "masked" which I think just hides what
the code is really doing. Why not just say "disable" ?

"Setting the DBGACK_MASK bit disables the watchdog outputs when the SoC is
  in debug mode. Debug mode is determined by the DBGACK CPU signal."

That seems to be much clearer to me, though I think there should still
be a comment along the line of "disable watchdog output if CPU is in
debug mode" in the code.

That doesn't really explain _why_ the watchdog is disabled in this mode,
but at least it makes it obvious what is happening.

>>
>>>     */
>>>    #define QUIRK_HAS_WTCLRINT_REG                      (1 << 0)
>>>    #define QUIRK_HAS_PMU_MASK_RESET            (1 << 1)
>>>    #define QUIRK_HAS_PMU_RST_STAT                      (1 << 2)
>>>    #define QUIRK_HAS_PMU_AUTO_DISABLE          (1 << 3)
>>>    #define QUIRK_HAS_PMU_CNT_EN                        (1 << 4)
>>> +#define QUIRK_HAS_DBGACK_BIT                 (1 << 5)
>>>
>>>    /* These quirks require that we have a PMU register map */
>>>    #define QUIRKS_HAVE_PMUREG \
>>> @@ -279,7 +284,7 @@ static const struct s3c2410_wdt_variant drv_data_gs101_cl0 = {
>>>        .cnt_en_reg = GS_CLUSTER0_NONCPU_OUT,
>>>        .cnt_en_bit = 8,
>>>        .quirks = QUIRK_HAS_PMU_RST_STAT | QUIRK_HAS_PMU_MASK_RESET | QUIRK_HAS_PMU_CNT_EN |
>>> -               QUIRK_HAS_WTCLRINT_REG,
>>> +               QUIRK_HAS_WTCLRINT_REG | QUIRK_HAS_DBGACK_BIT,
>>>    };
>>>
>>>    static const struct s3c2410_wdt_variant drv_data_gs101_cl1 = {
>>> @@ -291,7 +296,7 @@ static const struct s3c2410_wdt_variant drv_data_gs101_cl1 = {
>>>        .cnt_en_reg = GS_CLUSTER1_NONCPU_OUT,
>>>        .cnt_en_bit = 7,
>>>        .quirks = QUIRK_HAS_PMU_RST_STAT | QUIRK_HAS_PMU_MASK_RESET | QUIRK_HAS_PMU_CNT_EN |
>>> -               QUIRK_HAS_WTCLRINT_REG,
>>> +               QUIRK_HAS_WTCLRINT_REG | QUIRK_HAS_DBGACK_BIT,
>>>    };
>>>
>>>    static const struct of_device_id s3c2410_wdt_match[] = {
>>> @@ -408,6 +413,21 @@ static int s3c2410wdt_enable(struct s3c2410_wdt *wdt, bool en)
>>>        return 0;
>>>    }
>>>
>>> +static void s3c2410wdt_mask_dbgack(struct s3c2410_wdt *wdt, bool mask)
>>
>> I think I must be missing something. This is only ever called with mask==true,
>> meaning the bit, if present, is always set.
>>
>> Why not call the function s3c2410wdt_set_dbgack() and drop the unnecessary
>> parameter ?
> 
> I can update like you suggest, it would simplify the logic a little bit.
> 

Please do.

Thanks,
Guenter