Hi Brian,
On 03/09/2018 07:28 PM, Brian Norris wrote:
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 don't think it was intended behavior. We don't even know for sure (or at least
I don't know) if all implementations of this IP have the same configuration bit
layout. All we can do is hope for the best.
Still, clobbering just 1 bit is better than clobbering 30 bit.
Thanks,
Guenter
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
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