On 10/08/2015 05:44 AM, Hanjun Guo wrote: > On 10/08/2015 11:21 AM, kernel test robot wrote: >> FYI, we noticed the below changes on >> >> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master >> commit 7494b07ebaae2117629024369365f7be7adc16c3 ("ACPI: add in a >> bad_madt_entry() function to eventually replace the macro") >> >> [ 0.000000] ACPI: undefined MADT subtable type for FADT 4.0: 127 (length >> 12) > > Seems that the MADT table contains reserved subtable type (0x7F), > so this is traded as a wrong type in our patch. > >> [ 0.000000] ACPI: Error parsing LAPIC address override entry > > This was called by early_acpi_parse_madt_lapic_addr_ovr() in > arch/x86/kernel/acpi/boot.c, which is scanning MADT for the first > time when booting, so it will fail the boot process when finding > the reserved MADT subtable type. > >> [ 0.000000] ACPI: Invalid BIOS MADT, disabling ACPI > > As the spec said in Table 5-46 (ACPI 6.0): > > 0x10-0x7F Reserved. OSPM skips structures of the reserved type. > > Should we just ignore those reserved type when scanning the MADT > table? In the patch "ACPI: add in a bad_madt_entry() function to > eventually replace the macro", we just trade it as wrong, that's > why we failed to boot the system. > > Thanks > Hanjun
Arrgh. This is why people get frustrated with ACPI. The spec is saying that those sub-table types are reserved -- implying they can and probably will be used for something else in the future -- but then vendors are shipping firmware that uses those reserved values, and an OS *expects* them to be used, and there is *no* documentation of it other than a kernel workaround. So yet again, technically this MADT subtable *is* wrong, and someone should slap the vendor for doing this. But, the practical side of this is that we now have to workaround what is now a known violation of the spec. The more ACPI allows this kind of nonsense, the less usable it will become. At a minimum, whoever is responsible for this firmware needs to make sure the spec reflects what they are doing. In the meantime, the only option is what Hanjun suggests -- make this a warning and not a failure. I'll prepare a patch and attach it to a reply here in a few minutes... -- ciao, al ----------------------------------- Al Stone Software Engineer Linaro Enterprise Group al.st...@linaro.org ----------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
