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Message-ID: <20140221163302.GN16114@sgi.com> Date: Fri, 21 Feb 2014 10:33:02 -0600 From: Russ Anderson <rja@....com> To: "Zheng, Lv" <lv.zheng@...el.com> Cc: Matthew Garrett <matthew.garrett@...ula.com>, "lenb@...nel.org" <lenb@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "minyard@....org" <minyard@....org>, "rjw@...ysocki.net" <rjw@...ysocki.net>, "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org> Subject: Re: [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@...r.kernel.org [mailto:linux-acpi-owner@...r.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@....com > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-acpi" in > > the body of a message to majordomo@...r.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@....com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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