On Thu, Sep 10, 2020 at 07:51:05PM +0000, Derrick, Jonathan wrote: > On Thu, 2020-09-10 at 14:17 -0500, Bjorn Helgaas wrote: > > On Thu, Sep 10, 2020 at 06:52:48PM +0000, Derrick, Jonathan wrote: > > > On Thu, 2020-09-10 at 12:38 -0500, Bjorn Helgaas wrote: > > > > On Thu, Sep 10, 2020 at 04:33:39PM +0000, Derrick, Jonathan wrote: > > > > > On Wed, 2020-09-09 at 20:55 -0500, Bjorn Helgaas wrote: > > > > > > On Fri, Aug 21, 2020 at 08:32:20PM +0800, Kai-Heng Feng wrote: > > > > > > > New Intel laptops with VMD cannot reach deeper power saving state, > > > > > > > renders very short battery time. > > > > > > > > > > > > > > As BIOS may not be able to program the config space for devices under > > > > > > > VMD domain, ASPM needs to be programmed manually by software. This is > > > > > > > also the case under Windows. > > > > > > > > > > > > > > The VMD controller itself is a root complex integrated endpoint that > > > > > > > doesn't have ASPM capability, so we can't propagate the ASPM settings to > > > > > > > devices under it. Hence, simply apply ASPM_STATE_ALL to the links under > > > > > > > VMD domain, unsupported states will be cleared out anyway. > > > > > > > > > > > > > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx> > > > > > > > --- > > > > > > > drivers/pci/pcie/aspm.c | 3 ++- > > > > > > > drivers/pci/quirks.c | 11 +++++++++++ > > > > > > > include/linux/pci.h | 2 ++ > > > > > > > 3 files changed, 15 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c > > > > > > > index 253c30cc1967..dcc002dbca19 100644 > > > > > > > --- a/drivers/pci/pcie/aspm.c > > > > > > > +++ b/drivers/pci/pcie/aspm.c > > > > > > > @@ -624,7 +624,8 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist) > > > > > > > aspm_calc_l1ss_info(link, &upreg, &dwreg); > > > > > > > > > > > > > > /* Save default state */ > > > > > > > - link->aspm_default = link->aspm_enabled; > > > > > > > + link->aspm_default = parent->dev_flags & PCI_DEV_FLAGS_ENABLE_ASPM ? > > > > > > > + ASPM_STATE_ALL : link->aspm_enabled; > > > > > > > > > > > > This function is ridiculously complicated already, and I really don't > > > > > > want to make it worse. > > > > > > > > > > > > What exactly is the PCIe topology here? Apparently the VMD controller > > > > > > is a Root Complex Integrated Endpoint, so it's a Type 0 (non-bridge) > > > > > > device. And it has no Link, hence no Link Capabilities or Control and > > > > > > hence no ASPM-related bits. Right? > > > > > > > > > > That's correct. VMD is the Type 0 device providing config/mmio > > > > > apertures to another segment and MSI/X remapping. No link and no ASPM > > > > > related bits. > > > > > > > > > > Hierarchy is usually something like: > > > > > > > > > > Segment 0 | VMD segment > > > > > Root Complex -> VMD | Type 0 (RP/Bridge; physical slot) - Type 1 > > > > > | Type 0 (RP/Bridge; physical slot) - Type 1 > > > > > > > > > > > And the devices under the VMD controller? I guess they are regular > > > > > > PCIe Endpoints, Switch Ports, etc? Obviously there's a Link involved > > > > > > somewhere. Does the VMD controller have some magic, non-architected > > > > > > Port on the downstream side? > > > > > > > > > > Correct: Type 0 and Type 1 devices, and any number of Switch ports as > > > > > it's usually pinned out to physical slot. > > > > > > > > > > > Does this patch enable ASPM on this magic Link between VMD and the > > > > > > next device? Configuring ASPM correctly requires knowledge and knobs > > > > > > from both ends of the Link, and apparently we don't have those for the > > > > > > VMD end. > > > > > > > > > > VMD itself doesn't have the link to it's domain. It's really just the > > > > > config/mmio aperture and MSI/X remapper. The PCIe link is between the > > > > > Type 0 and Type 1 devices on the VMD domain. So fortunately the VMD > > > > > itself is not the upstream part of the link. > > > > > > > > > > > Or is it for Links deeper in the hierarchy? I assume those should > > > > > > just work already, although there might be issues with latency > > > > > > computation, etc., because we may not be able to account for the part > > > > > > of the path above VMD. > > > > > > > > > > That's correct. This is for the links within the domain itself, such as > > > > > between a type 0 and NVMe device. > > > > > > > > OK, great. So IIUC, below the VMD, there is a Root Port, and the Root > > > > Port has a link to some Endpoint or Switch, e.g., an NVMe device. And > > > > we just want to enable ASPM on that link. > > > > > > > > That should not be a special case; we should be able to make this so > > > > it Just Works. Based on this patch, I guess the reason it doesn't > > > > work is because link->aspm_enabled for that link isn't set correctly. > > > > > > > > So is this just a consequence of us depending on the initial Link > > > > Control value from BIOS? That seems like something we shouldn't > > > > really depend on. > Seems like a good idea, that it should instead be quirked if ASPM is > found unusable on a link. Though I'm not aware of how many platforms > would require a quirk.. > > > > > > > > That's the crux. There's always pcie_aspm=force. > > > Something I've wondered is if there is a way we could 'discover' if the > > > link is ASPM safe? > > > > Sure. Link Capabilities is supposed to tell us that. If aspm.c > > depends on the BIOS settings, I think that's a design mistake. > > > > But what CONFIG_PCIEASPM_* setting are you using? The default > > is CONFIG_PCIEASPM_DEFAULT, which literally means "Use the BIOS > > defaults". If you're using that, and BIOS doesn't enable ASPM below > > VMD, I guess aspm.c will leave it disabled, and that seems like it > > would be the expected behavior. > > > > Does "pcie_aspm=force" really help you? I don't see any uses of it > > that should apply to your situation. > > > > Bjorn > > No you're right. I don't think we need pcie_aspm=force, just the policy > configuration. I'm not sure where we're at here. If the kernel is built with CONFIG_PCIEASPM_DEFAULT=y (which means "use the BIOS defaults"), and the BIOS doesn't enable ASPM on these links below VMD, then Linux will leave things alone. I think that's working as intended. If desired, we should be able to enable ASPM using sysfs in that case. We have a pci_disable_link_state() kernel interface that drivers can use to *disable* ASPM for their device. But I don't think there's any corresponding interface for drivers to *enable* ASPM. Maybe that's an avenue to explore? Bjorn
