[PATCH u-boot-marvell] arm: mvebu: turris_omnia: enable A385 watchdog before disabling MCU watchdog

[Tom Rini]

On Fri, Nov 12, 2021 at 02:44:15PM +0100, Stefan Roese wrote:
> On 11/9/21 17:14, Marek Behún wrote:
> > From: Pali Rohár <pali at kernel.org>
> > 
> > Commit aeb0ca64dbb5 ("arm: mvebu: turris_omnia: disable MCU watchdog in
> > SPL when booting over UART") disabled MCU watchdog when booting over
> > UART to ensure that watchdog does not reboot the board before UART
> > transfer finishes.
> > 
> > But if UART transfer fails for some reason, or if U-Boot binary crashes,
> > then board hangs forever as there is no watchdog running which could
> > reset it.
> > 
> > To fix this issue, enable A385 watchdog with very high timeout before
> > disabling MCU watchdog to ensure that even slow transfer can finish
> > successfully before watchdog timer expires and also to ensure that if
> > board hangs for some reason, watchdog will reset it.
> > 
> > Omnia's MCU watchdog has fixed 120 seconds timer and it cannot be
> > changed (without updating MCU firmware). A385 watchdog by default uses
> > 25 MHz input clock and so the largest timeout value (2^32-1) can be
> > just 171 seconds. But A385 watchdog can be switched to use NBCLK (L2) as
> > input clock (on Turris Omnia it is 800 MHz clock) and in this case final
> > watchdog clock frequency is calculated as:
> > 
> >    freq = NBCLK / 2 / (2 ^ R)
> > 
> > So A385 watchdog on Turris Omnia can be configured to at most 1374
> > seconds (about 22 minutes). We set it to 10 minutes, which should be
> > enough even for bigger U-Boot binaries or slower UART transfers.
> > 
> > Both U-Boot and Linux kernel, when initializing A385 watchdog, switch
> > watchdog timer to 25 MHz input clock, so usage of NBCLK input clock in
> > U-Boot SPL does not cause any issues.
> > 
> > Fixes: aeb0ca64dbb5 ("arm: mvebu: turris_omnia: disable MCU watchdog in SPL when booting over UART")
> > Signed-off-by: Pali Rohár <pali at kernel.org>
> > Signed-off-by: Marek Behún <marek.behun at nic.cz>
> 
> I'm wondering if it makes sense to add this "slow" watchdog support to
> the common watchdog driver instead (orion_wdt.c). So that it dynamically
> configures the needed input clock for the desired timeout.
> 
> Would this be possible?

I know I'm late to the thread here, but why can't / aren't we servicing
the 120s watchdog during UART loading?  Or have I gone crazy and we
don't do that on say OMAP?

-- 
Tom
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 659 bytes
Desc: not available
URL: <https://lists.denx.de/pipermail/u-boot/attachments/20211112/a72b9279/attachment.sig>