On Thu, Jun 17, 2021 at 03:36:53PM +0300, Mika Westerberg wrote: > Some PCIe devices only support PME (Power Management Event) from D3cold. > One example is ASMedia xHCI controller: > > 11:00.0 USB controller: ASMedia Technology Inc. ASM1042A USB 3.0 Host Controller (prog-if 30 [XHCI]) > ... > Capabilities: [78] Power Management version 3 > Flags: PMEClk- DSI- D1- D2- AuxCurrent=55mA PME(D0-,D1-,D2-,D3hot-,D3cold+) > Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME- > > With such devices, if it has wake enabled, the kernel selects lowest > possible power state to be D0 in pci_target_state(). This is problematic > because it prevents the root port it is connected to enter low power > state too which makes the system consume more energy than necessary. IIUC this is because the loop that checks which states support PME starts with D3hot and doesn't even look at D3cold. > The problem in pci_target_state() is that it only accounts the "current" > device state, so when the bridge above it (a root port for instance) is > transitioned into D3hot the device transitions into D3cold. This is > because when the root port is first transitioned into D3hot then the > ACPI power resource is turned off which puts the PCIe link to L2/L3 (and > the root port and the device are in D3cold). If the root port is kept in > D3hot it still means that the device below it is still effectively in > D3cold as no configuration messages pass through. Furthermore the > implementation note of PCIe 5.0 sec 5.3.1.4 says that the device should > expect to be transitioned into D3cold soon after its link transitions > into L2/L3 Ready state. > > Taking the above into consideration, instead of forcing the device stay > in D0 we modify pci_target_state() to return D3hot in this special case > and make __pci_enable_wake() to enable PME too in this case. > > Reported-by: Utkarsh H Patel <utkarsh.h.patel@xxxxxxxxx> > Reported-by: Koba Ko <koba.ko@xxxxxxxxxxxxx> > Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> > --- > The previous version of the patch is here: > > https://lore.kernel.org/linux-pm/20210616150516.28242-1-mika.westerberg@xxxxxxxxxxxxxxx/ > > Changes from the previous version: > > * Dropped redundant test in pci_target_state(). > > drivers/pci/pci.c | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index b717680377a9..043c5c304308 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -2485,7 +2485,13 @@ static int __pci_enable_wake(struct pci_dev *dev, pci_power_t state, bool enable > if (enable) { > int error; > > - if (pci_pme_capable(dev, state)) > + /* > + * Enable PME if device is capable from given state. > + * Special case is device that can only generate PME > + * from D3cold then we enable PME too. > + */ > + if (pci_pme_capable(dev, state) || > + (state == PCI_D3hot && pci_pme_capable(dev, PCI_D3cold))) > pci_pme_active(dev, true); > else > ret = 1; > @@ -2595,6 +2601,14 @@ static pci_power_t pci_target_state(struct pci_dev *dev, bool wakeup) > * PME#. > */ > if (dev->pme_support) { > + /* > + * Special case if device supports only PME from > + * D3cold but not from D3hot we still return D3hot. > + */ > + if (target_state == PCI_D3hot && > + (dev->pme_support & (1 << PCI_D3cold))) > + return target_state; I've spent quite a bit of time trying to understand this, and I'm kind of dragging my feet on it because I haven't been able to really connect this with the specs. It also seems unfortunate to have to add this special case in two places. It seems like we're basically lying and *saying* we're going to put the device in D3hot, but due to some magic invisible assumption, we *actually* put it in D3cold. > while (target_state > && !(dev->pme_support & (1 << target_state))) > target_state--; Nit 1: "if (target_state == PCI_D3hot && ...) return target_state;" means "if (...) return PCI_D3hot;". When we're returning a constant value that we already know, I think it's clearer to use the constant. Nit 2: it looks like both these tests should use pci_pme_capable(), which would match the other special case in __pci_enable_wake().
