Hi Al, On Thu, Feb 05, 2015 at 05:11:31PM +0000, Al Stone wrote: > On 02/04/2015 09:43 AM, Lorenzo Pieralisi wrote: > > On Mon, Feb 02, 2015 at 12:45:39PM +0000, Hanjun Guo wrote: > >> From: Graeme Gregory <graeme.gregory@xxxxxxxxxx> > >> > >> There are two flags: PSCI_COMPLIANT and PSCI_USE_HVC. When set, > >> the former signals to the OS that the firmware is PSCI compliant. > >> The latter selects the appropriate conduit for PSCI calls by > >> toggling between Hypervisor Calls (HVC) and Secure Monitor Calls > >> (SMC). > >> > >> FADT table contains such information in ACPI 5.1, FADT table was > >> parsed in ACPI table init and copy to struct acpi_gbl_FADT, so > >> use the flags in struct acpi_gbl_FADT for PSCI init. > > > > So you do rely on a global FADT being available, if you use it for PSCI > > detection you can use it for ACPI revision detection too, right ? > > > > Point is, either we should not use the global FADT table, or we use > > it consistently, or there is something I am unaware of that prevents > > you from using in some code paths and I would like to understand > > why. > > The FADT is a required table for arm64, as noted in the documentation > and the SBBR. While unfortunately the spec does not say it is mandatory, > even x86 systems are pretty useless without it. So yes, we rely on it > being available, not only for the PSCI info, but other flags such as > HW_REDUCED_ACPI. > > I suppose it does not have to be globally scoped. However, the FADT is > frequently used, especially on x86, so it makes sense to me from an > efficiency standpoint to have a global reference to it. > > I'm not sure I understand what is meant by using FADT for ACPI revision > detection; there are fields in the FADT that provide a major and minor > number for the FADT itself, but I don't believe there's any guarantee > those will be the same as the level of the specification that is being > supported by the kernel (chances are they will, but it's not mandatory). > > I've probably just missed a part of a thread somewhere; could you point > me to where the inconsistency lies? I'm just not understanding right this > second.... Yes, it is my fault, I was referring to another thread/patch (9), where you need to check the FADT revision to "validate it" (ie >= 5.1) for the arm64 kernel. What I am saying is: if the global FADT is there to parse PSCI info, it is there to check the FADT revision too, I do not necessarily see the need for calling acpi_table_parse() again to do it, the FADT revision checking can be carried out as for PSCI, that's all I wanted to say. Thanks, Lorenzo -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
