hx20: restore RW firmware access

[DHowett]

This pull request comprises three bug fixes.

1. lfw: restore RW firmware access by using the right pin mux

The alternate function table for LFW on the hx20 contained a few
incorrect values that resulted in LFW being unable to read from flash,
which disabled the use of the RW (and in some cases the RO) firmware
image.

1. SHD_IO0 is function 1 on the MEC152x, not function 2.
2. SHD_IO2 and SHD_IO3 were not included in the alternate function table.

The alternate function table from hx20/gpio.inc is correct, but it is
missing the SPI alternate for SHD_GLK/GPIO_0056.

In the future, we may want to move to model where hx20/gpio.inc includes
hx20/lfw/gpio.inc and common pin configurations are shared.

2. Remember whether we cut power to ourselves, and re-check during boot

On the hx20 (and presumably hx30,) a design issue prevents us from
hibernating the EC properly. Therefore, every time we bring the machine
down we cut power instead of hibernating. That results in the next boot
being a complete reset.

There is code in lfw that checks whether the current boot is due to a
watchdog reset or a power-on reset and if it is, clears the image type
back to EC_IMAGE_UNKNOWN. Due to that design issue, the hx20 EC is
always in POR/VTR or WDT on startup.

By storing whether the last shutdown was graceful/intended and checking
it before resetting the image type, we can work around this issue.

3. Make sure we fire SHUTDOWN_COMPLETE hooks when the AP goes down

This ensures that the hook in common/system.c that triggers an
"at-shutdown" reboot from RO to RW fires.

The x86 power sequencer in $/power fires this hook, but we don't.

Without this, ectool reboot_ec RW at-shutdown doesn't work.

4. mchp/lfw: make sure we keep the EC on for long operations

Over the past six months with this patch set, I've observed one
troubling behavior: the laptop would not always boot when it was powered
completely off (with the EC off as well) and I clicked the power button.

It turns out that the power buttons control VCI_IN[01] and that the
VBAT-powered control interface is configured to drive GPIO250 as VCI_OUT
based on the status of those inputs. Now, GPIO250 is also known as EC_ON
on hx20/30: it controls whether 3VL_EC is on.

The MEC1521 manual recommends the following example of using VCI_OUT on
a "mobile platform" (abbreviated):

1. A coin cell battery is installed, powering VBAT
2. The power button on VCI_IN0# is pushed causing VCI_OUT to be
   asserted, powering the VTR rail
3. The EC reconfigures VCI so that firmware controls the VCI_OUT pin.

Now, the EC is doing this over in vci_task (hx20/hx30), which is long
after LFW has started and jumped to main firmware. The problem is,
restoring access to RO and RW images in the prior three commits causes
us to try to read from flash on startup.

Reading from flash is slightly slower, so we extend the period of time
between step 2 and 3 where 3VL_EC is only driven by VCI_IN0#. When the
user releases the power button during that window, 3VL_EC is cut and the
EC shuts down.

This patch fixes the issue by asserting firmware control of VCI_OUT as
early as is safe in lfw.

[DHowett]

I've updated this patch set with my tested and working proposal. It now properly (1) reboots into RW, (2) boots into RW from cold-off, and (3) can reboot into RO/RW at-shutdown

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[DHowett]

Nailed it. Here's the explanation -

mchp/lfw: make sure we keep the EC on for long operations

Over the past six months with this patch set, I've observed one
troubling behavior: the laptop would not always boot when it was powered
completely off (with the EC off as well) and I clicked the power button.

It turns out that the power buttons control VCI_IN[01] and that the
VBAT-powered control interface is configured to drive GPIO250 as VCI_OUT
based on the status of those inputs. Now, GPIO250 is also known as EC_ON
on hx20/30: it controls whether 3VL_EC is on.

The MEC1521 manual recommends the following example of using VCI_OUT on
a "mobile platform" (abbreviated):

1. A coin cell battery is installed, powering VBAT
2. The power button on VCI_IN0# is pushed causing VCI_OUT to be
   asserted, powering the VTR rail
3. The EC reconfigures VCI so that firmware controls the VCI_OUT pin.

Now, the EC is doing this over in vci_task (hx20/hx30), which is long
after LFW has started and jumped to main firmware. The problem is,
restoring access to RO and RW images in the prior three commits causes
us to try to read from flash on startup.

Reading from flash is slightly slower, so we extend the period of time
between step 2 and 3 where 3VL_EC is only driven by VCI_IN0#. When the
user releases the power button during that window, 3VL_EC is cut and the
EC shuts down.

This patch fixes the issue by asserting firmware control of VCI_OUT as
early as is safe in lfw.

[DHowett]

This might seem counterintuitive, but gpio_reset is documented as turning off alternative states for the GPIO and asserting the flags set in gpio.inc; this results in it being re-muxed as GPIO and pulled high.