On Mon, Sep 30, 2024, at 06:06, Nick Chan wrote:
> The Apple A8X SoC seems to be slowest at resetting, taking up to around
> 125ms to reset. Wait 150ms to be safe here.
>
> Reviewed-by: Sven Peter <sven@xxxxxxxxxxxxx>
> Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> Signed-off-by: Nick Chan <towinchenmi@xxxxxxxxx>
> ---
> drivers/watchdog/apple_wdt.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/watchdog/apple_wdt.c b/drivers/watchdog/apple_wdt.c
> index d4f739932f0b..353ecf0b04dc 100644
> --- a/drivers/watchdog/apple_wdt.c
> +++ b/drivers/watchdog/apple_wdt.c
> @@ -127,11 +127,11 @@ static int apple_wdt_restart(struct
> watchdog_device *wdd, unsigned long mode,
> /*
> * Flush writes and then wait for the SoC to reset. Even though the
> * reset is queued almost immediately experiments have shown that it
> - * can take up to ~20-25ms until the SoC is actually reset. Just wait
> - * 50ms here to be safe.
> + * can take up to ~120-125ms until the SoC is actually reset. Just
> + * wait 150ms here to be safe.
> */
> (void)readl_relaxed(wdt->regs + APPLE_WDT_WD1_CUR_TIME);
> - mdelay(50);
> + mdelay(150);
I think you also need to insert a barrier before the mdelay(),
or turn the readl_relaxed() into a readl(), it will otherwise
be bypassed by the delay.
The comment is a bit confusing here as it suggests that the
MMIO read is meant to serialize between the restart and the
mdelay(), but the _relaxed() annotation on the readl()
explicitly skips that serialization, so one of the two is
wrong here.
Arnd
