Re: [PATCH] usb: host: ehci: workaround PME bug on AMD EHCI controller

Bjorn Helgaas
2017-06-15T13:23:13Z

On Thu, Jun 15, 2017 at 03:02:25PM +0800, Kai-Heng Feng wrote:
> On Thu, Jun 15, 2017 at 2:55 AM, Alan Stern <stern@rowland.harvard.edu> wrote:
> > On Tue, 13 Jun 2017, Bjorn Helgaas wrote:
> >
> >> [+cc Rafael, linux-pm]
> >>
> >> On Tue, Jun 13, 2017 at 12:21:15PM +0800, Kai-Heng Feng wrote:
> >> > On Mon, Jun 12, 2017 at 10:18 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> >> > > Let's get some help from people who understand PCI well.
> >> > >
> >> > > Here's the general problem: Kai-Heng has a PCI-based USB host
> >> > > controller that advertises wakeup capability from D3, but it doesn't
> >> > > assert PME# from D3 when it should. For "lspci -vv" output, see
> >> > >
> >> > > http://marc.info/?l=linux-usb&m=149570231732519&w=2
> >> > >
> >> > > On Mon, 12 Jun 2017, Kai-Heng Feng wrote:
> >> > >
> >> > >> On Mon, Jun 12, 2017 at 3:04 PM, Kai-Heng Feng
> >> > >> <kai.heng.feng@canonical.com> wrote:
> >> > >> > On Fri, Jun 9, 2017 at 10:43 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> >> > >> >> On Fri, 9 Jun 2017, Kai-Heng Feng wrote:
> >> > >> >>
> >> > >> >> Is this really the right solution? Maybe it would be better to allow
> >> > >> >> the controller to go into D3 provided no wakeup signal is needed. You
> >> > >> >> could do:
> >> > >> >>
> >> > >> >> device_set_wakeup_capable(&pdev->dev, 0);
> >> > >> >
> >> > >> > This doesn't work.
> >> > >> > After applying this function, still nothing happens when devices get plugged in.
> >> > >> > IIUC this function disable the wakeup function, but what I want to do
> >> > >> > here is to have PME signal works even when runtime PM is enabled.
> >> > >
> >> > > This may indicate a bug in either the PCI or USB stacks (or both!). If
> >> > > a driver requires wakeup capability from runtime suspend but the device
> >> > > does not provide it, the PCI core should not allow the device to go
> >> > > into runtime suspend. Or is that the driver's responsibility?
> >> > >
> >> > >> > I also saw some legacy PCI PM stuff, so I also tried:
> >> > >> > device_set_wakeup_capable(&pdev->dev, 1);
> >> > >> > ...doesn't work either.
> >> > >> >
> >> > >> >>
> >> > >> >> Another alternative is to put the controller into D2 instead of D3, but
> >> > >> >> (1) I don't know how to do that, and (2) we don't know if wakeup
> >> > >> >> signalling works any better in D2 than it does in D3.
> >> > >> >
> >> > >> > I'll try if D2 works.
> >> > >>
> >> > >> Put the device into D2 instead of D3 can make the wakeup signaling
> >> > >> work, i.e. USB devices can be correctly detected after plugged into
> >> > >> EHCI port.
> >> > >>
> >> > >> Do you think this alternative an acceptable workaround?
> >> > >
> >> > > Yes, it is. The difficulty is that I don't know how to tell the PCI
> >> > > core that the device should go in D2 during runtime suspend instead of
> >> > > D3. Some sort of quirk may be needed -- perhaps Bjorn can help.
> >
> >> The lspci output [1] shows:
> >>
> >> 00:12.0 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB EHCI Controller (rev 39) (prog-if 20 [EHCI])
> >> Capabilities: [c0] Power Management version 2
> >> Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0+,D1+,D2+,D3hot+,D3cold+)
> >> Status: D3 NoSoftRst- PME-Enable+ DSel=0 DScale=0 PME-
> >> Bridge: PM- B3+
> >>
> >> The device claims it can assert PME# from D3hot. If it can't, that
> >> sounds like a hardware defect that should be addressed with a quirk.
> >> Ideally we would also have a pointer to the AMD hardware erratum.
> >>
> >> Is the following path involved here?
> >>
> >> pci_finish_runtime_suspend
> >> target_state = pci_target_state()
> >> if (device_may_wakup())
> >> if (dev->pme_support)
> >> ...
> >> pci_set_power_state(..., target_state)
> >>
> >> If so, I would naively expect that a quirk could clear the
> >> PCI_PM_CAP_PME_D3 and PCI_PM_CAP_PME_D3cold bits in dev->pme_support,
> >> and pci_target_state() would then avoid selecting D3 or D3cold. But
> >> I'm not an expert in power management.
> >
> > That's a good idea. However, we should apply the quirk only when it is
> > needed. Which means we need to know the numeric values for the PCI
> > IDs. Also, this will help searching for published errata.
> >
> > Kai-Heng, what does "lspci -nvs 00:12.0" show?
>
> 00:12.0 0c03: 1022:7808 (rev 39) (prog-if 20 [EHCI])
> Subsystem: 1028:0732
> Flags: bus master, 66MHz, medium devsel, latency 32, IRQ 18
> Memory at fe769000 (32-bit, non-prefetchable) [size=256]
> Capabilities: [c0] Power Management version 2
> Capabilities: [e4] Debug port: BAR=1 offset=00e0
> Kernel driver in use: ehci-pci
>
> Here's the diff that can make it work:
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 1a14ca8965e6..7bd278535ab3 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2208,6 +2208,12 @@ void pci_pm_init(struct pci_dev *dev)
> }
>
> pmc &= PCI_PM_CAP_PME_MASK;
> +
> + if (unlikely(dev->vendor == 0x1022 && dev->device == 0x7808))
> {
> + dev_info(&dev->dev, "PME# does not work under D3,
> disabling it\n");
> + pmc &= ~(PCI_PM_CAP_PME_D3 | PCI_PM_CAP_PME_D3cold);
> + }
> +
> if (pmc) {
> dev_printk(KERN_DEBUG, &dev->dev,
> "PME# supported from%s%s%s%s%s\n",
>
> If you think this is OK, I'll resend the patch.

Thanks for checking this out!

My suggestion:

- Open a bug report at bugzilla.kernel.org, Drivers/PCI component,
attach "lspci -vv" output for entire system.

- Reorganize your diff above as a "final" quirk that updates
dev->pme_support and puts a note in dmesg. I think this could go
in arch/x86/pci/fixup.c since I think this is only possible on
x86.

- Include the bug URL, errata URL, and "Description" and "Potential
Effect on System" text in your changelog.

Bjorn