On Thu, Nov 9, 2023 at 5:31 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Thu, Nov 09, 2023 at 05:06:15PM -0500, Jim Quinlan wrote: > > ... > > > BTW, besides the RPi4, I haven't been able to find a Linux platform > > where I can do > > > > echo $POLICY > /sys/module/pcie_aspm/parameters/policy > > This sounds like something we should fix. What exactly happens? I > think this should be handled at pcie_aspm_set_policy(), so: Well, I've tried changing the ASPM policy on my x86 Ubuntu system and IIRC a Fedora system. In both cases it says "illegal write operation" but I am root and the "policy" file does have rw perms for root, so I have no idea how it comes back with that error. Some machines allow one to change the setting in the BIOS , FWIW. Right now on my CM4, "echo $POLICY > policy" actually works. Perhaps when I was testing this I did not yet apply my commits, or perhaps it was with a specific endpoint device. Regardless, I'll let you know with a backtrace if I see this again. Regards, Jim > > /sys/module/pcie_aspm/parameters/policy doesn't exist (seems > unlikely)? > > Returns -EPERM (would indicate aspm_disabled)? > > Returns -EINVAL (would indicate $POLICY doesn't match anything in > policy_str[])? > > Returns 0 with no action (would indicate $POLICY is the same as the > current aspm_policy)? > > > It seems that the FW/ACPI typically locks this down. I did see a > > comment somewhere that > > said that the reason it was locked down is because too many devices > > cannot handle it. > > Do you have any details about FW/ACPI locking this down? > aspm_disabled is set by the kernel "pcie_aspm=off" parameter (I assume > you're not referring to this), if the FADT has ACPI_FADT_NO_ASPM set, > or if a host bridge's _OSC is missing or failed (maybe [1] is the > comment you saw?) > > These all *should* be unusual cases, so I'd be surprised if you're > tripping over one of these. I would NOT be surprised if we had some > issue in pcie_config_aspm_link() or pcie_set_clkpm() that meant the > policy change didn't work as intended, though. > > Bjorn > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/acpi/pci_root.c?id=v6.6#n617 >
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