Hi,
On Fri, Mar 09, 2018 at 07:20:38PM -0800, Guenter Roeck wrote:
> On 03/09/2018 06:44 PM, Brian Norris wrote:
> > RK3399 has rst_pulse_length in CONTROL_REG[4:2], determining the length
> > of pulse to issue for system reset. We shouldn't clobber this value,
> > because that might make the system reset ineffective. On RK3399, we're
> > seeing that a value of 000b (meaning 2 cycles) yields an unreliable
> > (partial?) reset, and so we only fully reset after the watchdog fires a
> > second time. If we retain the system default (010b, or 8 clock cycles),
> > then the watchdog reset is much more reliable.
> >
> > Read-modify-write retains the system value and improves reset
> > reliability.
> >
> > Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> > ---
> > drivers/watchdog/dw_wdt.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
> > index c2f4ff516230..6925d3e6c6b3 100644
> > --- a/drivers/watchdog/dw_wdt.c
> > +++ b/drivers/watchdog/dw_wdt.c
> > @@ -34,6 +34,7 @@
> > #define WDOG_CONTROL_REG_OFFSET 0x00
> > #define WDOG_CONTROL_REG_WDT_EN_MASK 0x01
> > +#define WDOG_CONTROL_REG_RESP_MODE_MASK 0x02
> > #define WDOG_TIMEOUT_RANGE_REG_OFFSET 0x04
> > #define WDOG_TIMEOUT_RANGE_TOPINIT_SHIFT 4
> > #define WDOG_CURRENT_COUNT_REG_OFFSET 0x08
> > @@ -124,11 +125,16 @@ static int dw_wdt_set_timeout(struct watchdog_device *wdd, unsigned int top_s)
> > static int dw_wdt_start(struct watchdog_device *wdd)
> > {
> > struct dw_wdt *dw_wdt = to_dw_wdt(wdd);
> > + u32 val;
> > dw_wdt_set_timeout(wdd, wdd->timeout);
> > - writel(WDOG_CONTROL_REG_WDT_EN_MASK,
> > - dw_wdt->regs + WDOG_CONTROL_REG_OFFSET);
> > + val = readl(dw_wdt->regs + WDOG_CONTROL_REG_OFFSET);
> > + /* Disable interrupt mode; always perform system reset. */
> > + val &= ~WDOG_CONTROL_REG_RESP_MODE_MASK;
>
> You don't talk about this change in the description.
I guess I could mention it. I was assuming that was an intended behavior
of the existing driver: that we set resp_mode=0 (via clobber), so we
always get a system reset (we don't try to handle any interrupt in this
driver).
I'll include something along those lines in the commit message.
> > + /* Enable watchdog. */
> > + val |= WDOG_CONTROL_REG_WDT_EN_MASK;
> > + writel(val, dw_wdt->regs + WDOG_CONTROL_REG_OFFSET);
> > return 0;
> > }
> >
>
> Similar code is in dw_wdt_restart(), where it may be equally or even
> more important. Granted, only if the watchdog isn't running, but still...
Oh, I misread that code. It looked like an read/modify/write already,
but it was actually just a read/check/write. I should fix that, since
otherwise the restart will clobber the very thing I'm trying to fix
here, which might actually make the intended machine restart quite
ineffective.
Thanks,
Brian
--
To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
