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uart_dev_ns8250: Switch ACPI UART subtype for Marvell SoCs
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Authored by mw on May 21 2021, 3:43 PM.

Details

Summary

DBG2 ACPI table description [1] specifies three subtypes
related to 16550 UART:
0x0 - 16550 compatible
0x1 - 16550 subset
0x12 - 16550 compatible with parameters defined in Generic Address Structure (GAS)

It turned out however, that the Windows OS treats 0x0 subtype as
legacy x86 UART with 8-bit access. ARM SoCs can use types 0x1 (16550 with
fixed mmio32 access) or 0x12 (16550 with fully respected GAS contents).

Switch Marvell SoCs ACPI UART subtype to 0x1 - thanks to that the same firmware
can run properly with UART output in FreeBSD, Windows 10, Linux and ESXI
hypervisor. Tests showed the older firmware versions that use 0x0
UART subtype in SPCR table continue to display output properly.

[1] https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/acpi-debug-port-table

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Event Timeline

mw requested review of this revision.May 21 2021, 3:43 PM
mw created this revision.
This revision was not accepted when it landed; it landed in state Needs Review.Jun 2 2021, 8:05 AM
This revision was automatically updated to reflect the committed changes.