The ACPI Specification defines a Generic Address Structure (GAS),
which is used to describe UART controller register layout in the
SPCR table. The driver responsible for parsing it (uart_cpu_acpi)
wrongly associates the Access Size field to the uart_bas's regshft
and the register BitWidth to the regiowidth - according to
the definitions it should be opposite.
This problem remained hidden most likely because the majority of platforms
use 32-bit registers (BitWidth) which are accessed with the according
size (Dword). However on Marvell Armada 8k / Cn913x platforms,
the 32-bit registers should be accessed with Byte granulity, which
unveiled the issue.
This patch fixes above by proper values assignment and slightly improved
parsing.
Note that handling of the AccessWidth set to EFI_ACPI_6_0_UNDEFINED is
needed to work around a buggy SPCR table on EC2 x86 "bare metal" instances.
Reviewed by: manu, imp, cperciva, greg_unrelenting.technology
Obtained from: Semihalf
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D25373
This takes the SPCR code currently in uart_cpu_arm64.c, moves it into
a new uart_cpu_acpi.c (with some associated refactoring), and uses it
from both arm64 and x86.
An SPCR serial port address AccessWidth field value of 0 ("reserved")
is now treated as 1 ("byte access") in order to work around a buggy
SPCR table on Amazon EC2 i3.metal instances.
Reviewed by: manu, Greg V
MFC after: 3 days
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D20357
