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    SubjectRe: [PATCH V2] Change ACPI IPMI support to "default y"
    On Fri, Feb 21, 2014 at 02:17:12AM +0000, Zheng, Lv wrote:
    > Hi,
    >
    > Sorry for interrupting you.
    > I have some information that may be helpful for your discussion.
    > Please find them in the inlined replies.
    > Well, I don't want to join the fight, just for your informations. :-)

    I don't want to join the fight, either.

    I have not looked at your code changes but the description
    looks like the right direction.


    > > From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi-owner@vger.kernel.org] On Behalf Of Russ Anderson
    > > Sent: Friday, February 21, 2014 7:59 AM
    > >
    > > On Thu, Feb 20, 2014 at 11:09:42PM +0000, Matthew Garrett wrote:
    > > > On Thu, 2014-02-20 at 16:45 -0600, Russ Anderson wrote:
    > > > > On Thu, Feb 20, 2014 at 10:26:45PM +0000, Matthew Garrett wrote:
    > > >
    > > > > > Because I'm trying to ensure that the default behaviour of the kernel is
    > > > > > to *work*. Defaulting to having IPMI be modular means that the default
    > > > > > behaviour of the kernel, as far as the ACPI spec goes, is to be broken.
    > > > >
    > > > > The ACPI spec requires IPMI functionality before a module loads at
    > > > > boot time? And the kernel is *broken* if it does not support ACIP IPMI
    > > > > functionality before module load time? Really?
    > > >
    > > > There's no mechanism to ensure that IPMI support will be loaded before
    > > > ACPI calls attempt to access IPMI operation regions. Really.
    > >
    > > And no mechanism can be added to ensure that ACPI call are
    > > not attempted before IPMI is initialized? A flag or lock
    > > or exported symbol indicating IPMI support is ready.
    >
    > In fact there is a workaround solution I've posted here:
    > https://patchwork.kernel.org/patch/2831851/
    > The updated version of this patch can be found at:
    > https://bugzilla.kernel.org/attachment.cgi?id=112611
    > It is the acpi-ipmi13.patch file.
    >
    > This solution may change the meaning of ACPI spec defined _REG.
    > So we may need a better solution.
    >
    > But after merging this patch, it is safe to unload acpi_ipmi at users' wishes.
    > Without solutions to solve region handler uninstallation races, it is not safe to unload acpi_ipmi module.
    > You can see crashes in the description of this patch.
    >
    > The ipmi_si module is using a different way to unload itself which has not been tested by me.
    > You can find it in Documentation/IPMI.txt by searching "hot and remove of interfaces" in this file.
    >
    > >
    > > > > > ACPI 4.0 includes support for IPMI operation regions. Modular IPMI means
    > > > > > that the kernel will spend a significant amount of time (potentially
    > > > > > until a user manually loads a driver) failing to implement part of the
    > > > > > IPMI specification. That's a problem, and the correct fix is to ensure
    > > > > > that the kernel always implements IPMI support.
    > > > >
    > > > > The ACPI spec says ipmi_si cannot be a driver? Really?
    > > > > What is the real problem you are trying to solve?
    > > >
    > > > The most straightforward case is that of an ACPI power meter.
    > >
    > > So it is just a matter of making sure ipmi_si modules loads before
    > > the ACPI power meter module loads, right? module dependency issue.
    >
    > I agree.
    > I think there should be relationship between ACPI region and Linux kernel modules.
    > In fact on the well-known operating system, _REG is always invoked at the end of the IRP_PNP_START_DEVICE completions.
    > But we may still be able to return -EPROBE_DEFER in the power meter driver when it detects failures caused by the readiness state of the region handlers.
    >
    > I didn't work further on this issue when solving the reported bug:
    > https://bugzilla.kernel.org/show_bug.cgi?id=46741
    >
    > >
    > > > Several
    > > > vendors implement this with an IPMI operation region. Calling any of the
    > > > power meter functions will trigger access to that IPMI operation region,
    > > > which will fail. This may result in driver initialisation failing. There
    > > > is no express dependency between the power meter driver and ipmi_si,
    > > > because the spec envisages IPMI support as basic kernel functionality.
    > > > It's meant to be there before you start loading any other drivers.
    > >
    > > The spec "envisages"? I get there is a dependency, that IPMI driver
    > > needs to be loaded before ACIP power meter. This isn't the first
    > > case of a driver being dependent on another driver. That doesn't
    > > mean IPMI driver must be built into the kernel.
    > >
    > > > > > Now, you've described some other problems. I don't disagree that those
    > > > > > are problems. The correct thing for us to do with those problems is to
    > > > > > fix them, not to simply change the kernel defaults such that it's
    > > > > > possible for users to choose between two differently broken states. I'm
    > > > > > absolutely willing to help, as long as you're willing to put some
    > > > > > reasonable amount of effort into describing them.
    > > > >
    > > > > How about ACPI IPMI functionality starts when the ipmi_si
    > > > > module loads at boot time.
    >
    > Actually, I have a solution implemented this.
    > You can find it at:
    > https://bugzilla.kernel.org/attachment.cgi?id=112611
    > It is the acpi-ipmi14.patch file.
    >
    > The patch will hand the maintenance-ship of acpi_ipmi to IPMI community.
    > I'm not sure it is proper to merge it by Linux upstreams.
    >
    > Thanks and best regards
    > -Lv
    >
    > > >
    > > > I've repeatedly asked for you to provide detailed descriptions of the
    > > > problems you've seen because I have a genuine interest in fixing them.
    > > > If you're just going to childishly refuse then this discussion is
    > > > pointless.
    > >
    > > The distro cases I would point you at are marked private.
    > > And you do not have access to our internal support system.
    > > A simple google search for "kipmi0" shows a lot of reports of
    > > high cpu utilization.
    > >
    > > And I'm old enough to appreciate being called childishly. :-)
    > >
    > > --
    > > Russ Anderson, Kernel and Performance Software Team Manager
    > > SGI - Silicon Graphics Inc rja@sgi.com
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at http://vger.kernel.org/majordomo-info.html

    --
    Russ Anderson, Kernel and Performance Software Team Manager
    SGI - Silicon Graphics Inc rja@sgi.com


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