PCIe, power management, and problematic BIOSes

Posted Jun 29, 2011 18:16 UTC (Wed) by flewellyn (subscriber, #5047)
In reply to: PCIe, power management, and problematic BIOSes by mjg59
Parent article: PCIe, power management, and problematic BIOSes

I see. So, is there a way for the OS to test for this ASPM support without recourse to the BIOS?

PCIe, power management, and problematic BIOSes

Posted Jun 29, 2011 18:28 UTC (Wed) by mjg59 (subscriber, #23239) [Link] (5 responses)

Not really. In an ideal world hardware that broke with ASPM simply wouldn't advertise ASPM support, but doing that was actually a spec violation until recently. So you're left with hardware advertising ASPM support and you have no way of knowing whether or not it's safe to touch that, and in some cases *turning off* ASPM can cause hardware to explode as well. So you either need complete knowledge of all hardware where ASPM is broken, or you need to assume that the BIOS will give you reliable information as to whether or not ASPM works on that platform.

PCIe, power management, and problematic BIOSes

Posted Jun 29, 2011 20:06 UTC (Wed) by samroberts (subscriber, #46749) [Link] (2 responses)

But how does the BIOS know whether ASPM works or not?

If it figures out from the devices, the kernel could do this, too.

Since you say the kernel can't do this reliably, I assume the BIOS authors have to hard-code this information about the devices? I guess, in theory, they should know, but it sounds pretty horrible.

PCIe, power management, and problematic BIOSes

Posted Jun 29, 2011 20:13 UTC (Wed) by mjg59 (subscriber, #23239) [Link]

Because the BIOS has been tested with that set of hardware. This is typically a laptop problem, not a desktop one.

PCIe, power management, and problematic BIOSes

Posted Jun 29, 2011 20:24 UTC (Wed) by dlang (guest, #313) [Link]

because the bios engineer hard-coded it to say if it works or not.

the BIOS isn't testing things and deciding it doesn't work, it's a hard-coded entry made by the BIOS programmer.

PCIe, power management, and problematic BIOSes

Posted Jun 29, 2011 20:40 UTC (Wed) by flewellyn (subscriber, #5047) [Link] (1 responses)

So we have a situation in which the firmware lies to you, and then penalizes you if you believe it? What a wonderful world.

PCIe, power management, and problematic BIOSes

Posted Jun 29, 2011 21:00 UTC (Wed) by mjg59 (subscriber, #23239) [Link]

Not an uncommon situation, sadly.