Hi Quentin,

On Fri, Sep 23, 2022 at 10:25:58AM +0200, Quentin Schulz wrote:

Hi Jeff,

On 9/22/22 19:20, Jeff LaBundy wrote:

quoted

Hi Quentin,

On Thu, Sep 22, 2022 at 12:12:09PM +0200, Quentin Schulz wrote:

quoted

From: Quentin Schulz <redacted>

This event code represents the firmware source to use at boot.
Value 0 means using "standard" firmware source, value 1 means using
"alternative" firmware source.

For example, some hardware has the ability to force the BOOTROM to load
the bootloader from a secondary firmware source (say SD card) instead of
trying with the standard first and then the secondary. This event allows
the userspace to know which firmware source was requested *in hardware*.

Signed-off-by: Quentin Schulz <redacted>

This does not seem like the right approach, especially since the switch
can easily be flipped after the state is already latched.

If the bootloader needs to pass information to the kernel (boot source or
otherwise), a safer and more flexible approach is to share some variables
in eMMC, or pass information using the kernel cmdline.

I made a terrible job at explaining what this switch is for, sorry.

Obviously, the state of the switch cannot represent which firmware boot
source was used as only the bootloader will be able to tell (since it
usually tries storage media in a specific order and the primary boot source
could get corrupted at one point in time). Anyway, like you rightfully
stated, this is useless "info" and the important one would be passed by the
bootloader to the kernel (possibly via Device Tree fixup in case of
Aarch64). U-Boot does this to set the memory node so this could be done
again with a different property or something like that. Anyways, not
something I'm really interested in.

I have a switch on my devkit which implements the BOOT_ALT#/BIOS_DISABLE#
functionality from the Q7 standard, see section 3.1.17 Miscellaneous Signals
in the specs:
https://sget.org/wp-content/uploads/2018/09/Qseven-Spec_2.1.pdf

"""
BIOS_DISABLE#
/BOOT_ALT#
Module BIOS disable input signal. Pull low to disable
module's on-board BIOS. Allows off-module BIOS
implementations. This signal can also be used to disable
standard boot firmware flash device and enable an alternative
boot firmware source, for example a boot loader.
"""

This is basically the configuration of the firmware boot source to use for
*the next boot*. It does not represent which boot source was used, nor which
one will effectively be used.

In our case, this switch electrically disables eMMC and SPI flashes and only
allow to boot from SD card (this switch is then electrically overridden by
another GPIO at runtime by the bootloader/Linux kernel, but the state of the
switch is still available to the user via another GPIO).

Thanks for the additional detail and the use-case is quite clear; I just
don't think input is the right home for this. Input makes more sense for
switches that a user may change during runtime with the expectation that
an event handler effects some sort of response.

Such is the case for lid open/close and headphone insertion, but here we
are just interested in the state of a muxed GPIO.

I have this switch on the board and I want to expose its state to the user,
if this new event code is not possible/a good idea what would you suggest we
could use?

Note that we already support the same switch but in a different way: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/rockchip/rk3399-puma-haikou.dts#n167
We are just configuring the GPIOs into the GPIO mode with a pull-up, and
then it's up to the user to use gpiod or gpio-sysfs to check the state of
the GPIO used for this switch. I don't like this, very not user-friendly and
was looking for something better :)

Actually, that's exactly what I was going to suggest. What in particular
is not user-friendly about it?

Of course, this is just my opinion as a fellow customer of input and it
is ultimately up to Dmitry.

Hope I explained myself a bit better this time, lemme know if I can clarify
anything.

Thanks!
Quentin

Kind regards,
Jeff LaBundy

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