On Thursday, March 5, 2020 1:24:25 PM CET Jan Engelhardt wrote: > The value in "new" is constructed from "old" such that all bits defined > as reserved by the ACPI spec[1] are left untouched. But if those bits > do not happen to be all zero, "new < 3" will not evaluate to true. > > The firmware of the laptop(s) Medion MD63490 / Akoya P15648 comes with > garbage inside the "FACS" ACPI table. The starting value is > old=0x4944454d, therefore new=0x4944454e, which is >= 3. Mask off > the reserved bits. > > [1] https://uefi.org/sites/default/files/resources/ACPI_6_2.pdf > > References: https://bugzilla.kernel.org/show_bug.cgi?id=206553 > Signed-off-by: Jan Engelhardt <jengelh@xxxxxxx> > --- > arch/x86/kernel/acpi/boot.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c > index 04205ce127a1..f9e84a0e2fa2 100644 > --- a/arch/x86/kernel/acpi/boot.c > +++ b/arch/x86/kernel/acpi/boot.c > @@ -1740,7 +1740,7 @@ int __acpi_acquire_global_lock(unsigned int *lock) > new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1)); > val = cmpxchg(lock, old, new); > } while (unlikely (val != old)); > - return (new < 3) ? -1 : 0; > + return ((new & 0x3) < 3) ? -1 : 0; > } > > int __acpi_release_global_lock(unsigned int *lock) > Applied as 5.7 material, thanks!
