Hi, Rafael and Dan > From: Dan Williams [mailto:dan.j.williams@xxxxxxxxx] > Subject: Re: [PATCH 08/11] ACPICA: Tables: Back port acpi_get_table_with_size() and > early_acpi_os_unmap_memory() from Linux kernel > > On Thu, Dec 8, 2016 at 5:18 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > On Thu, Dec 8, 2016 at 2:11 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > >> On Tue, Nov 29, 2016 at 11:21 PM, Lv Zheng <lv.zheng@xxxxxxxxx> wrote: > >>> ACPICA commit cac6790954d4d752a083e6122220b8a22febcd07 > >>> > >>> This patch back ports Linux acpi_get_table_with_size() and > >>> early_acpi_os_unmap_memory() into ACPICA upstream to reduce divergences. > >>> > >>> The 2 APIs are used by Linux as table management APIs for long time, it > >>> contains a hidden logic that during the early stage, the mapped tables > >>> should be unmapped before the early stage ends. > >>> > >>> During the early stage, tables are handled by the following sequence: > >>> acpi_get_table_with_size(); > >>> parse the table > >>> early_acpi_os_unmap_memory(); > >>> During the late stage, tables are handled by the following sequence: > >>> acpi_get_table(); > >>> parse the table > >>> Linux uses acpi_gbl_permanent_mmap to distinguish the early stage and the > >>> late stage. > >>> > >>> The reasoning of introducing acpi_get_table_with_size() is: ACPICA will > >>> remember the early mapped pointer in acpi_get_table() and Linux isn't able to > >>> prevent ACPICA from using the wrong early mapped pointer during the late > >>> stage as there is no API provided from ACPICA to be an inverse of > >>> acpi_get_table() to forget the early mapped pointer. > >>> > >>> But how ACPICA can work with the early/late stage requirement? Inside of > >>> ACPICA, tables are ensured to be remained in "INSTALLED" state during the > >>> early stage, and they are carefully not transitioned to "VALIDATED" state > >>> until the late stage. So the same logic is in fact implemented inside of > >>> ACPICA in a different way. The gap is only that the feature is not provided > >>> to the OSPMs in an accessible external API style. > >>> > >>> It then is possible to fix the gap by providing an inverse of > >>> acpi_get_table() from ACPICA, so that the two Linux sequences can be > >>> combined: > >>> acpi_get_table(); > >>> parse the table > >>> acpi_put_table(); > >>> In order to work easier with the current Linux code, acpi_get_table() and > >>> acpi_put_table() is implemented in a usage counting based style: > >>> 1. When the usage count of the table is increased from 0 to 1, table is > >>> mapped and .Pointer is set with the mapping address (VALIDATED); > >>> 2. When the usage count of the table is decreased from 1 to 0, .Pointer > >>> is unset and the mapping address is unmapped (INVALIDATED). > >>> So that we can deploy the new APIs to Linux with minimal effort by just > >>> invoking acpi_get_table() in acpi_get_table_with_size() and invoking > >>> acpi_put_table() in early_acpi_os_unmap_memory(). Lv Zheng. > >>> > >>> Link: https://github.com/acpica/acpica/commit/cac67909 > >>> Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx> > >>> Signed-off-by: Bob Moore <robert.moore@xxxxxxxxx> > >> > >> This commit in -next (071b39575679 ACPICA: Tables: Back port > >> acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux > >> kernel) causes a regression in my nfit/nvdimm test environment. The > >> nfit produced by QEMU no longer results in a nvdimm bus being created. > >> > >> I have not root caused it, but I'm using the following command line > >> options to create an nfit in qemu-2.6. Reverting the commit leads > >> compile failures. > > > > Would the build problems go away if you reverted "ACPICA: Tables: > > Allow FADT to be customized with virtual address" (linux-next commit > > cf334d3174f9) in addition to it? > > Yes, reverting those two commits gets me back to a functional environment: > > Revert "ACPICA: Tables: Allow FADT to be customized with virtual address" > Revert "ACPICA: Tables: Back port acpi_get_table_with_size() and > early_acpi_os_un To Dan: It seems in drivers/acpi/nfit/core.c. The returned table size is used by the NFIT code. I think it should be changed to use table_header->length. To Rafael: I can offer a quick fix for this by returning table_header->length from acpi_get_table_with_size(). Thanks and best regards Lv ��.n��������+%������w��{.n�����{�����ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
