Re: [PATCH v3 12/14] rtc: pcf2127: support generic watchdog timing configuration

Philipp Rosenberger <p.rosenberger@xxxxxxxxxx> · Fri, 20 Jan 2023 09:06:31 +0100

On 19.01.23 18:48, Hugo Villeneuve wrote:
On Wed, 18 Jan 2023 14:23:14 +0100
Philipp Rosenberger <p.rosenberger@xxxxxxxxxx> wrote:

Hi Philipp,
you are right that the value store/computed inside the structure wdd (struct watchdog_device) should be in seconds, according to the header file documentation in watchdog.h.

However, in the PCF2127 datasheet, the value n that is stored in the PCF2127_REG_WD_VAL register does not represent a value in seconds, but a counter value. It is given by this equation:

     n = source_clock_frequency x timer_period_in_seconds

For the PCF2127, since the clock used is 1Hz, it works as the previous equation can be simplified as:

     n = timer_period_in_seconds

However, if the source clock is different than 1Hz, it would no longer work. Also, since the PCF2131 uses a default clock of 1/4 Hz, it also would not work.

That is the reason why I modified the watchdog timer value (n) computation to take the clock into account. I then use the desired timeout in seconds given by  PCF2127_WD_VAL_DEFAULT to compute the counter value (n).

So what I am proposing to do is to store the PCF2127_WD_VAL_DEFAULT value in wdd->timeout, as before, but convert it to a counter value in pcf2127_wdt_active_ping(). Or to only compute it once, I could define a new variable and compute/set it in pcf2127_watchdog_init().

Hugo.


Hi Hugo,

with some small changes to your code I was able to get the behavior 
right. But with this the timeout get converted from seconds to the 
counter register format on every ping.

Just add WD_COUNTER(wdd->timeout, pcf2127->cfg->wdd_clock_hz_x1000) to 
the regmap_write() in pcf2127_wdt_ping(). Then in 
pcf2127_watchdog_init() just do:

pcf2127->wdd.timeout = PCF2127_WD_VAL_DEFAULT;

Best regards,
Philipp


On 15.12.22 16:02, Hugo Villeneuve wrote:
From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>

Introduce in the configuration structure two new values to hold the
watchdog clock source and the min_hw_heartbeat_ms value.

The minimum and maximum timeout values are automatically computed from
the watchdog clock source value for each variant.

The PCF2131 has no 1Hz watchdog clock source, as is the case for
PCF2127/29.

The next best choice is using a 1/4Hz clock, giving a watchdog timeout
range between 4 and 1016s. By using the same register configuration as
for the PCF2127/29, the 1/4Hz clock source is selected.

Note: the PCF2127 datasheet gives a min/max range between 1 and 255s,
but it should be between 2 and 254s, because the watchdog is triggered
when the timer value reaches 1, not 0.

Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
---
   drivers/rtc/rtc-pcf2127.c | 56 +++++++++++++++++++++++++++++++++------
   1 file changed, 48 insertions(+), 8 deletions(-)

diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
index 11fbdab6bf01..3fd2fee4978b 100644
--- a/drivers/rtc/rtc-pcf2127.c
+++ b/drivers/rtc/rtc-pcf2127.c
@@ -157,9 +157,29 @@

   /* Watchdog timer value constants */
   #define PCF2127_WD_VAL_STOP               0
-#define PCF2127_WD_VAL_MIN         2
-#define PCF2127_WD_VAL_MAX         255
-#define PCF2127_WD_VAL_DEFAULT             60
+#define PCF2127_WD_VAL_DEFAULT             60 /* In seconds. */
+/* PCF2127/29 watchdog timer value constants */
+#define PCF2127_WD_CLOCK_HZ_X1000  1000 /* 1Hz */
+#define PCF2127_WD_MIN_HW_HEARTBEAT_MS     500
+/* PCF2131 watchdog timer value constants */
+#define PCF2131_WD_CLOCK_HZ_X1000  250  /* 1/4Hz */
+#define PCF2131_WD_MIN_HW_HEARTBEAT_MS     4000
+/*
+ * Compute watchdog period, t, in seconds, from the WATCHDG_TIM_VAL register
+ * value, n, and the clock frequency, f, in Hz.
+ *
+ * The PCF2127/29 datasheet gives t as:
+ *   t = n / f
+ * The PCF2131 datasheet gives t as:
+ *   t = (n - 1) / f
+ * For both variants, the watchdog is triggered when the WATCHDG_TIM_VAL reaches
+ * the value 1, and not zero. Consequently, the equation from the PCF2131
+ * datasheet seems to be the correct one for both variants.
+ */
+#define WD_PERIOD_S(_n_, _f1000_) ((1000 * ((_n_) - 1)) / (_f1000_))
+
+/* Compute value of WATCHDG_TIM_VAL to obtain period t, in seconds. */
+#define WD_COUNTER(_t_, _f1000_) ((((_t_) * (_f1000_)) / 1000) + 1)

   /* Mask for currently enabled interrupts */
   #define PCF2127_CTRL1_IRQ_MASK (PCF2127_BIT_CTRL1_TSF1)
@@ -202,6 +222,11 @@ struct pcf21xx_config {
     u8 reg_wd_val; /* Watchdog value register. */
     u8 reg_clkout; /* Clkout register. */
     u8 reg_reset;  /* Reset register if available. */
+
+   /* Watchdog configuration. */
+   int wdd_clock_hz_x1000; /* Value in Hz multiplicated by 1000 */
+   int wdd_min_hw_heartbeat_ms;
+
     unsigned int ts_count;
     struct pcf21xx_ts_config ts[4];
     struct attribute_group attribute_group;
@@ -496,10 +521,19 @@ static int pcf2127_watchdog_init(struct device *dev, struct pcf2127 *pcf2127)
     pcf2127->wdd.parent = dev;
     pcf2127->wdd.info = &pcf2127_wdt_info;
     pcf2127->wdd.ops = &pcf2127_watchdog_ops;
-   pcf2127->wdd.min_timeout = PCF2127_WD_VAL_MIN;
-   pcf2127->wdd.max_timeout = PCF2127_WD_VAL_MAX;
-   pcf2127->wdd.timeout = PCF2127_WD_VAL_DEFAULT;
-   pcf2127->wdd.min_hw_heartbeat_ms = 500;
+
+   pcf2127->wdd.min_timeout =
+           WD_PERIOD_S(2, pcf2127->cfg->wdd_clock_hz_x1000);
+   pcf2127->wdd.max_timeout =
+           WD_PERIOD_S(255, pcf2127->cfg->wdd_clock_hz_x1000);
+   pcf2127->wdd.timeout = WD_COUNTER(PCF2127_WD_VAL_DEFAULT,
+                                     pcf2127->cfg->wdd_clock_hz_x1000);
+
+   dev_dbg(dev, "%s min = %ds\n", __func__, pcf2127->wdd.min_timeout);
+   dev_dbg(dev, "%s max = %ds\n", __func__, pcf2127->wdd.max_timeout);
+   dev_dbg(dev, "%s def = %d\n", __func__, pcf2127->wdd.timeout);
+
+   pcf2127->wdd.min_hw_heartbeat_ms = pcf2127->cfg->wdd_min_hw_heartbeat_ms;
     pcf2127->wdd.status = WATCHDOG_NOWAYOUT_INIT_STATUS;

     watchdog_set_drvdata(&pcf2127->wdd, pcf2127);
@@ -926,6 +960,8 @@ static struct pcf21xx_config pcf21xx_cfg[] = {
             .reg_wd_ctl = PCF2127_REG_WD_CTL,
             .reg_wd_val = PCF2127_REG_WD_VAL,
             .reg_clkout = PCF2127_REG_CLKOUT,
+           .wdd_clock_hz_x1000 = PCF2127_WD_CLOCK_HZ_X1000,
+           .wdd_min_hw_heartbeat_ms = PCF2127_WD_MIN_HW_HEARTBEAT_MS,
             .ts_count = 1,
             .ts[0] = {
                     .regs_base = PCF2127_REG_TS1_BASE,
@@ -951,6 +987,8 @@ static struct pcf21xx_config pcf21xx_cfg[] = {
             .reg_wd_ctl = PCF2127_REG_WD_CTL,
             .reg_wd_val = PCF2127_REG_WD_VAL,
             .reg_clkout = PCF2127_REG_CLKOUT,
+           .wdd_clock_hz_x1000 = PCF2127_WD_CLOCK_HZ_X1000,
+           .wdd_min_hw_heartbeat_ms = PCF2127_WD_MIN_HW_HEARTBEAT_MS,
             .ts_count = 1,
             .ts[0] = {
                     .regs_base = PCF2127_REG_TS1_BASE,
@@ -977,6 +1015,8 @@ static struct pcf21xx_config pcf21xx_cfg[] = {
             .reg_wd_val = PCF2131_REG_WD_VAL,
             .reg_clkout = PCF2131_REG_CLKOUT,
             .reg_reset  = PCF2131_REG_SR_RESET,
+           .wdd_clock_hz_x1000 = PCF2131_WD_CLOCK_HZ_X1000,
+           .wdd_min_hw_heartbeat_ms = PCF2131_WD_MIN_HW_HEARTBEAT_MS,
             .ts_count = 4,
             .ts[0] = {
                     .regs_base = PCF2131_REG_TS1_BASE,
@@ -1215,7 +1255,7 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,

     /*
      * Watchdog timer enabled and reset pin /RST activated when timed out.
-    * Select 1Hz clock source for watchdog timer.
+    * Select 1Hz clock source for watchdog timer (1/4Hz for PCF2131).
      * Note: Countdown timer disabled and not available.
      * For pca2129, pcf2129 and pcf2131, only bit[7] is for Symbol WD_CD
      * of register watchdg_tim_ctl. The bit[6] is labeled



--
Hugo Villeneuve <hugo@xxxxxxxxxxx>






