On 01/15/2015 09:10 AM, Grant Likely wrote: > On Tue, Jan 6, 2015 at 1:59 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> On Tuesday 06 January 2015 11:20:01 Catalin Marinas wrote: >>> On Mon, Jan 05, 2015 at 08:16:30PM +0000, Arnd Bergmann wrote: >>>> On Monday 05 January 2015 13:13:02 Catalin Marinas wrote: >>>>>> since passing no DT tables to OS but >>>>>> acpi=force is missing is a corner case, we can do a follow up patch to >>>>>> fix that, does it make sense? >>>>> >>>>> Not entirely. Why would no dtb and no acpi=force be a corner case? I >>>>> thought this should be the default when only ACPI tables are passed, no >>>>> need for an additional acpi=force argument. >>>> >>>> We don't really support the case of only ACPI tables for now. The expectation >>>> is that you always have working DT support, at least for the next few years >>>> as ACPI features are ramping up, and without acpi=force it should not try >>>> to use ACPI at all. >>> >>> So if both DT and ACPI are present, just use DT unless acpi=force is >>> passed. So far I think we agree but what I want to avoid is always >>> mandating acpi=force even when the DT tables are missing (in the long >>> run). >>> >>> Now, what's preventing a vendor firmware from providing only ACPI >>> tables? Do we enforce it in some way (arm-acpi.txt, kernel warning etc.) >>> that both DT and ACPI are supported, or at least that dts files are >>> merged in the kernel first? >> >> We have no way of enforcing what a board vendor ships, so if they want >> to have ACPI-only machines for MS Windows, they just won't work by >> default on Linux. Once ACPI support is mature enough, we can also >> have a whitelist or a different default for using it automatically >> when no DT is present. >> >> For drivers merged upstream, I would insist that every driver merged >> for an ARM64 platform has a documented DT binding that is used in the >> driver. > > That's a dumb rule. It will result in untested DT code paths being > thrown into drivers just too meet the rules rather than on whether or > not they will actually be used. It's fine to allow driver authors to > only implement the ACPI code path if that is what they are working > with. We can *always* add a DT path to the driver when it is needed. It gets worse. There *will* be large numbers of ACPI only ARM servers landing over the coming year. Not only would DT code be untested, but insisting on keeping e.g. a DSDT and DT in sync is never going to work anyway. Already we have early stage servers that contain a DT used for bringup that is subsequently not being updated as often as the ACPI tables (those systems are now booting exclusively in labs with ACPI). Eventually, I am going to push for the DT data to be removed from these systems rather than have out of date unmaintained DT data in firmware. Jon. -- 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
