Re: [PATCH 1/2] driver/aspeed-wdt: fix pretimeout for counting down logic

Really sorry for this mail and previous noisy mails; my thunderbird client must be misconfigured to send out mail for command + s shortcut when I wanted to save draft...

Heyi

On 2025/2/19 11:40, Heyi Guo wrote:

Hi Guenter,

Thanks for your comments.

On 2025/2/18 13:33, Guenter Roeck wrote:

quoted

On 2/17/25 19:16, Heyi Guo wrote:

quoted

Aspeed watchdog uses counting down logic, so the value set to register
should be the value of subtracting pretimeout from total timeout.

Fixes: 9ec0b7e06835 ("watchdog: aspeed: Enable pre-timeout interrupt")

Signed-off-by: Heyi Guo <redacted>

Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Andrew Jeffery <andrew@codeconstruct.com.au>
Cc: Eddie James <eajames@linux.ibm.com>
---
  drivers/watchdog/aspeed_wdt.c | 7 +++++++
  1 file changed, 7 insertions(+)

diff --git a/drivers/watchdog/aspeed_wdt.c b/drivers/watchdog/aspeed_wdt.c
index b4773a6aaf8c..520d8aba12a5 100644
--- a/drivers/watchdog/aspeed_wdt.c
+++ b/drivers/watchdog/aspeed_wdt.c

@@ -187,6 +187,13 @@ static int aspeed_wdt_set_pretimeout(struct watchdog_device *wdd,
      u32 actual = pretimeout * WDT_RATE_1MHZ;
      u32 s = wdt->cfg->irq_shift;
      u32 m = wdt->cfg->irq_mask;
+    u32 reload = readl(wdt->base + WDT_RELOAD_VALUE);
+

It is unusual to use a register value here and not the configured timeout
value. I would have assumed that pretimeout is compared against wdt->timout,
not against the register value, and that the multiplication with WDT_RATE_1MHZ
is done after validation. This needs an explanation.

It was supposed to be a straight-forward way to check if the pretimeout value is
supported by the hardware. I can change to wdt->timeout if it is better.

Further, in the case of wdt->timeout > max_hw_heartbeat_ms, shall we restrict
the pretimeout to be larger than wdt->timeout - max_hw_heartbeat_ms  / 2? For
the watchdog_kworker works in max_hw_heartbeat_ms  / 2 interval, pretimeout
event may be triggered unexpected when watchdog is not pinged in
(max_hw_heartbeat_ms - (timeout - pretimeout)).

quoted

quoted

+    if (actual >= reload)
+        return -EINVAL;
+

On top of that, you'll also need to explain why watchdog_pretimeout_invalid()
and with it the validation in watchdog_set_pretimeout() does not work for this
watchdog and why this extra validation is necessary.

watchdog_pretimeout_invalid() will return false if wdt->timeout == 0, but we
can't determine the hardware pretimeout value if timeout == 0 here.

quoted

Guenter

quoted

+    /* watchdog timer is counting down */
+    actual = reload - actual;
        wdd->pretimeout = pretimeout;
      wdt->ctrl &= ~m;