The following messages are seen when booting chromeos-4.14 on Cyan.

[    1.870641] acpi 80862288:00: Device [PWM1] is in always present list
[    1.872825] ioremap error for 0x0-0x1000, requested 0x2, got 0x0

where 0x2 refers to nocache memory (as requested), and 0x0 is writeback memory.

ACPI source (from coreboot, src/soc/intel/braswell/acpi/lpss.asl):

Device (PWM1)
{
        Name (_HID, "80862288")
        Name (_UID, 1)
        Name (_DDN, "PWM Controller #1")

        Name (RBUF, ResourceTemplate()
        {
                Memory32Fixed (ReadWrite, 0, 0x1000, BAR0)
        })

        Method (_CRS)
        {
                CreateDwordField (^RBUF, ^BAR0._BAS, RBAS)
                Store (\SAB0, RBAS)
                Return (^RBUF)
        }

        Method (_STA)
        {
                If (LEqual (\SAEN, 1)) {
                        Return (0xF)
                } Else {
                        Return (0x0)
                }
        }
}

PWM1 is supposed to be used for backlight control. It is unknown if the problem has any practical impact.