-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Dan Kotowski
Sent: Monday, September 16, 2019 4:44 AM
To: [email protected]
Subject: Patch AML or patch acpi driver?
The _BST method in my laptop's AML only returns the present state, present
capacity, and present charge/discharge rate of the battery, but does not return
the present voltage across the terminals. Is it better to patch the AML or the
acpi driver to account for this missing DWORD?
As per the ACPI 2 spec (here:
https://uefi.org/sites/default/files/resources/ACPI_2.pdf), the BST method
should return the following struct:
Package {
Battery State //DWORD
Battery Present Rate //DWORD
Battery Remaining Capacity //DWORD
Battery Present Voltage //DWORD
}
However, when I look at the AML dumped from my controller, I can see that PKG0
as returned by the _BST method (line 10557 here:
https://gist.github.com/agrajag9/f91a09cc181c9df404a93d119316aa18) only has the
first 3 values and will never return the present voltage.
So the options are:
1. Patch the AML: This should be simple enough by copying either the DWORD or
logic for getting the Design Voltage in the _BIF method. I can imagine
scenarios where this causes issues for code attempting to compare the design
and present voltages checking for failing batteries, but right now the other 3
values just get ignored completely which is also less-than-useful.
If possible, I would do this, even if the actual value is unavailable;
Otherwise, the ACPICA code will always flag this as an error, since the length
of the package is incorrect.
2. Patch the driver: This would allow more platforms to handle incomplete BST
data, but it would complicate the driver logic some. In
sys/dev/acpica/acpi_battery.c the acpi_battery_bst_valid function checks for
state, capacity, and voltage, but not rate. Even if the design philosophy is
"all or nothing", then this is also bad logic. I think it would be better to
return true if ANY _BST DWORD is valid (not 0xFFFFFFFF) rather than failing if
some are invalid. This would at least expose the valid fields to the rest of
the system.
Dan Kotowski
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