Re: [PATCH v4] PCI/PM: Target PM state is D3hot if device can only generate PME from D3cold

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On Thu, Jun 17, 2021 at 2:36 PM Mika Westerberg
<mika.westerberg@xxxxxxxxxxxxxxx> 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.
>
> 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>

All of my comments have been addressed, so

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
> 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;
> +
>                         while (target_state
>                               && !(dev->pme_support & (1 << target_state)))
>                                 target_state--;
> --
> 2.30.2
>



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