Hi,

From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi-owner@vger.kernel.org] On Behalf Of Matthew Garrett
Sent: Saturday, February 22, 2014 12:13 AM

On Fri, 2014-02-21 at 02:17 +0000, Zheng, Lv wrote:

quoted

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.

I don't think that solves the underlying problem? We're still left with
no guarantee of ordering between ACPI IPMI operation region support
being available and the loading of a driver that may rely on it.

Yes. As it is a bit far beyond the bug report, I didn't work on it.
But actually, I have solution to achieve this.

quoted

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.

We don't have a guarantee that it'll happen at probe time. The
capabilities list may be static, and so we'll get our first failure on
an attempted userspace access instead.

This is the issue related to the IPMI operation region, and it can be solved by a "request_module()" call.
The -EPROBE_DEFER I mentioned is about the quality of  acpi power meter driver itself.

It may be that Corey's suggestion satisfies the concerns Russ raised.
Building IPMI in but only probing by default on systems that declare a
BMC in ACPI or DMI should avoid boot-time delays while still ensuring
that the functionality is available on systems where there's a real
chance that the firmware expects the OS to provide support.

If you take a look at this patch (https://patchwork.kernel.org/patch/2831851/), you'll see it is possible to add request_module() in acpi_region_default_handler().
The callback is invoked when the first IPMI region access happens and it is in the process context without any locking.
I'd rather to embed acpi_ipmi into ipmi_si module with this fix:
https://bugzilla.kernel.org/attachment.cgi?id=112611 (acpi-ipmi14.patch).
After that, a request_module() invocation of ipmi_si in acpi_region_default_handler() can solve what you are worrying about.

What's your opinion?

Thanks and best regards
-Lv

--
Matthew Garrett [off-list ref]