On Thu, Feb 05, 2015 at 10:47:23AM +0000, Ard Biesheuvel wrote: > On 5 February 2015 at 10:41, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > On Wed, Feb 04, 2015 at 06:58:14PM +0000, Mark Salter wrote: > >> On Wed, 2015-02-04 at 17:57 +0000, Catalin Marinas wrote: > >> > On Wed, Feb 04, 2015 at 04:08:27PM +0000, Mark Salter wrote: > >> > > acpi_os_remap() is used to map ACPI tables. These tables may be in ram > >> > > which are already included in the kernel's linear RAM mapping. So we > >> > > need ioremap_cache to avoid two mappings to the same physical page > >> > > having different caching attributes. > >> > > >> > What's the call path to acpi_os_ioremap() on such tables already in the > >> > linear mapping? I can see an acpi_map() function which already takes > >> > care of the RAM mapping case but there are other cases where > >> > acpi_os_ioremap() is called directly. For example, > >> > acpi_os_read_memory(), can it be called on both RAM and I/O? > >> > >> acpi_map() is the one I've seen. > > > > By default, if should_use_kmap() is not patched for arm64, it translates > > to page_is_ram(); acpi_map() would simply use a kmap() which returns the > > current kernel linear mapping on arm64. > > > >> I'm not sure about others. > > > > Question for the ARM ACPI guys: what happens if you implement > > acpi_os_ioremap() on arm64 as just ioremap()? Do you get any WARN_ON() > > (__ioremap_caller() checks whether the memory is RAM)? > > Regardless of whether you hit any WARN_ON()s now, Actually following the WARN_ON(), ioremap() returns NULL, so it may not go entirely unnoticed. > we still need to distinguish between MMIO ranges with device > semantics, and ACPI or other tables whose data may not be naturally > aligned all the time, and hence requiring memory semantics. > acpi_os_ioremap() may be used for both, afaik Is acpi_os_ioremap() called directly (outside acpi_map()) to map RAM that already part of the kernel linear memory? If yes, then I agree that we need to do such check. Another question, can we distinguish, in the ACPI core code, whether the mapping is for an ACPI table in RAM or some I/O space? -- Catalin -- 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
