[edk2] SP805 driver

Leif Lindholm leif.lindholm at linaro.org
Mon Dec 17 04:55:19 PST 2018

Hi Sami, Thomas, (and others on cc)

NXP are upstreaming a set containing an implementation of
EFI_WATCHDOG_TIMER_ARCH_PROTOCOL using a hardware watchdog as backing.
This idea comes from the SP805
driver ArmPlatformPkg/Drivers/SP805WatchdogDxe, which does the same.

The problem is that this is a horrible idea. The point of
the EFI_WATCHDOG_TIMER_ARCH_PROTOCOL is that it lets you schedule software
events when the watchdog timer expires. However, the SP805 driver does not
let you do this:

SP805RegisterHandler (
  IN EFI_WATCHDOG_TIMER_NOTIFY                NotifyFunction
  // ERROR: This function is not supported.
  // The hardware watchdog will reset the board

>From section 12.14 of the PI 1.6 spec:
"If no handler has been registered, or the registered handler returns, then
the system will be reset by calling the Runtime Service ResetSystem()."
Blatantly, any driver that does the above (and initializes hardware that
will reset the system without software control) will violate this.

Meanwhile, the only two ARM platforms that include this driver are TC2 and

Now, NXP are not at fault for following examples given to them in the
reference ARM driver section - but can we please keep further people from
making the same mistake?
So my question to {Sami|Thomas} is - can we nuke this driver, and if so,
can you provide the patches to remove it from edk2 and the resulting ones
needed for edk2-platforms?

I have no issues with reintroducing a fixed SP805 driver in the future that
does not claim to conform to the above protocol.

Finally - both the D03 and D05 platform .dsc files, as well as the
Hisilicon ArmPlatformLib, contain references to it. (Ming/Heyi - please
provide a patch.)


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