Torvalds: Investigating ACPI Problems

Sep 25, 2007

In a post on the Linux Kernel mailing list, Thomas Gleixner claims to have fixed ACPI suspend and resume problems. Linus Torvalds praised him for doing so, but also has his doubts.

"Sorry, it took me quite a while to realize the real root cause of the VAIO - and probably many other machines - suspend/resume regressions, which were unearthed by the dyntick / clockevents patches.", Thomas Gleixner explains, referring to two patches, aimed to resolve the suspend error that Andrew Morton noticed on his Vaio notebook.

The first developer to respond was Linus Torvalds. He praised the patches - "Ok, so the patches look fine," but goes on to criticize Gleixner in the same sentence, "but I somehow have this slight feeling that you gave up a bit too soon on the "*why* does this happen?" question." Torvalds then goes on to answer the question himself: "I realize that the answer is easily "because ACPI screwed up". Torvalds guesses that the patches don't actually fix the problem, but just work around it: "Because we don't necessarily understand what the real background for the problem is, I'm not sure we can say that it is solved."

Torvalds also assumes that the kernel completes the preparations for Suspend mode, and that ACPI triggers the right steps. But the "stupid firmware" doesn't expect any further calls to achieve low power status. And this is where Torvalds sees problems. Despite this, he is still going to apply the patches as is, even though he would feel better if he understood why.

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