RE: [RFC PATCH 02/10] acpi: install SSDT tables from initrd

[Zheng, Lv]

Hi,

> From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Octavian Purdila
> Subject: Re: [RFC PATCH 02/10] acpi: install SSDT tables from initrd
> 
> On Tue, Apr 5, 2016 at 3:49 AM, Zheng, Lv <lv.zheng@xxxxxxxxx> wrote:
> > Hi,
> >
> >> From: Octavian Purdila [mailto:octavian.purdila@xxxxxxxxx]
> >> Subject: Re: [RFC PATCH 02/10] acpi: install SSDT tables from initrd
> >>
> >> On Fri, Apr 1, 2016 at 1:11 PM, Octavian Purdila
> >> <octavian.purdila@xxxxxxxxx> wrote:
> >> > On Fri, Apr 1, 2016 at 8:05 AM, Zheng, Lv <lv.zheng@xxxxxxxxx> wrote:
> >> >> Hi,
> >> >>
> >> >> IMO, there is already a similar function upstreamed:
> >> >>
> >>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c85c
> >> c81
> >> >> Could it work for your use case?
> >> >
> >> > Yes, it is basically the same.
> >> >
> >> > The only difference is on how we handle taint. I think we should use a
> >> > new taint for overlays and that we don't need to disable lockdep.
> >> >
> >> > BTW, why is lockdep disabled when we override?
> >>
> >> The other thing I forgot to mention is that I think we should allow
> >> installing new tables even if CONFIG_ACPI_INITRD_TABLE_OVERRIDE is not
> >> selected. IMO the override and overlay functionality is different,
> >> with the latter being more then a debug option.
> > [Lv Zheng]
> > I don't think so. The initrd override mechanism is not dependent on
> CONFIG_ACPI_DEBUG.
> > According to the spec, we can allow a higher versioning same table (same
> table sig, table id, table oem id) to override the old tables as a patching
> functionality.
> > So both the functionalities are not debug options and serve for the same
> purpose from this point of view.
> > And IMO that's why the initrd override mechanism needn't be dependent on
> CONFIG_ACPI_DEBUG.
> >
> 
> The problem is that CONFIG_ACPI_INITRD_TABLE_OVERRIDE is presented as
> a debug option in Documentation/initrd_table_override.txt and most
> distributions are not selecting it which makes it hard to use it in
> practice.
> 
> > I'm really OK with removing the acpi_table_taint() for
> CONFIG_ACPI_INITRD_TABLE_OVERRIDE but leaving some info messages
> indicating the table upgrades.
> > I don't think this mechanism is unsafe.
> > It happens during a initialization step occurring before the table is loaded and
> hence should be safe even the synchronization is not so robust in ACPICA.
> > And with the revision support added, we should be able to allow vendors to
> update the buggy tables.
> > That means the tables may be originated from the safe sources - the vendors.
> >
> >>
> >> I will prepare a patch for the next version of the series to decouple
> >> installing new tables from CONFIG_ACPI_INITRD_TABLE_OVERRIDE.
> > [Lv Zheng]
> > I don't think they need to be decoupled.
> > The use case is:
> > If there is an ACPI table in initrd image and:
> > 1. if the table's revision is higher than the existing one, override the existing
> one;
> > 2. if the table is a brand new one, install it.
> >
> 
> The implementation will stay the same of course, I was just suggesting
> to move CONFIG_ACPI_INITRD_TABLE_OVERRIDE in
> acpi_os_physical_table_override to allow new tables to be loaded even
> if the option is not selected.
[Lv Zheng] 
This sounds reasonable.
Or you can rename it to CONFIG_ACPI_TABLE_UPGRADE and make it default 'y'.
Also you need to remove acpi_table_taint() which is not so useful now.

Thanks and best regards
-Lv