On 09/11/2016 10:50, Stephen Warren wrote:
On 11/09/2016 04:43 AM, Alexander Graf wrote:
On 07/11/2016 22:26, Stephen Warren wrote:
On 11/06/2016 03:24 AM, Alexander Graf wrote:
On 05/11/2016 23:01, Stephen Warren wrote:
On 11/02/2016 03:36 AM, Alexander Graf wrote:
The rpi has a pretty simple way of resetting the whole system. All it
takes
is to poke a few registers at a well defined location in MMIO space.
This patch adds support for the EFI loader implementation to allow an
OS to
reset and power off the system when we're outside of boot time.
(As an aside, I'm not sure why someone wanting EFI wouldn't just use a
complete EFI implementation such as TianoCore.)
diff --git a/arch/arm/mach-bcm283x/reset.c
b/arch/arm/mach-bcm283x/reset.c
+__efi_runtime_data struct bcm2835_wdog_regs *wdog_regs =
+ (struct bcm2835_wdog_regs *)BCM2835_WDOG_PHYSADDR;
+
+void __efi_runtime reset_cpu(ulong addr)
{
- struct bcm2835_wdog_regs *regs =
- (struct bcm2835_wdog_regs *)BCM2835_WDOG_PHYSADDR;
I'm not sure why that change is required. The value of the variable is
the same in both cases?
Take a look a few lines down in the patch:
+void efi_reset_system_init(void)
+{
+ efi_add_runtime_mmio(&wdog_regs, sizeof(*wdog_regs));
+}
What this does is register a *pointer* as run time service pointer.
What
does that mean?
When we enter RTS, Linux can map any region in the EFI memory map
into a
different place in its own virtual memory map. So any pointers we use
inside RTS have to be relocated to the new locations.
For normal relocations, we move the relocations from linker time to run
time, so that we can relocate ourselves when Linux does the switch-over
to a new address space.
However, for MMIO that's trickier. That's where the
efi_add_runtime_mmio() function comes into play. It takes care of
adding
the page around the references address to the EFI memory map as RTS
MMIO
and relocates the pointer when Linux switches us into the new address
space.
Does that explain why we need to move from an inline address to an
address stored in a memory location?
So EFI RTS runs in the same exception level as the rich OS, and not in
EL3? I would have expected EFI to run in EL3 with a completely separate
MMU configuration. If that's not the case, then this part of the patch
does make sense.
Right, it runs in EL2/EL1 with a virtual memory layout that is provided
by the OS.
Perhaps it's trying to ensure that if this gets compiled into an ldr
instruction, the referenced data value is in a linker section that's
still around when EFI runs? If so fine, but how is that ensured for
all
the other constants that this code uses, and if that happens
automatically due to the __efi_runtime marker above, why doesn't it
work
for this one constant?
Does U-Boot have a halt/poweroff/shutdown shell command? If so, it
might
be nice to enable it as part of this series, since the code to perform
that operation is now present.
That's what I originally wanted, yes :). Unfortunately due to the
relocation explained above, it's basically impossible for any reset
function that calls into MMIO space.
However, we do have it now for PSCI. If you have a PSCI enabled system,
we don't need to call into MMIO space and thus make the common reset
function available as RTS.
Can't the same U-Boot function be called both (a) during U-Boot runtime,
where wdog_regs are pre-initialized to match U-Boot's MMU configuration,
and (b) once the OS has booted, where wdog_regs has been modified
according to the new memory map?
That's exactly what this patch does, no?
I assume not, since you said just a few lines above that doing so was
impossible, hence why it doesn't implement any halt/poweroff/shutdown
shell commands.
So this patch transforms the code in a way that allows us to call the
same function from boot time (1:1 map) as well as run time
(non-voluntary map). I thought that's what you were suggesting.
Either way, does the approach make sense to you now?
Alex
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