Re: [PATCH v3 1/5] PCI: host-common: Add helper to determine host bridge D3cold eligibility

[Manivannan Sadhasivam]

On Wed, Mar 11, 2026 at 03:56:46PM +0530, Krishna Chaitanya Chundru wrote:
> Add a common helper, pci_host_common_d3cold_possible(), to determine
> whether a PCI host bridge can safely transition to D3cold.
> 

Host bridge cannot be transitioned to D3Cold, it can only transition the
devices to D3Cold state. You need to reword it throughout the patch.

> This helper is intended to be used by PCI host controller drivers to
> decide whether they may safely put the host bridge into D3cold based on
> the power state and wakeup capabilities of downstream endpoints.
> 
> The helper walks all devices on the bridge's primary bus

What do you mean by 'primary bus' here?  The helper is supposed to walk through
all busses starting from the Root bus, no?

> and only allows
> the host bridge to enter D3cold if all PCIe endpoints are already in
> PCI_D3hot. This ensures that we do not power off the host bridge while
> any active endpoint still requires the link to remain powered.
> 
> For devices that may wake the system, the helper additionally requires
> that the device supports PME wake from D3cold (via WAKE#). Devices that
> do not have wakeup enabled are not restricted by this check and do not
> block the host bridge from entering D3cold.
> 
> Devices without a bound driver and with PCI not enabled via sysfs are
> treated as inactive and therefore do not prevent the host bridge from
> entering D3cold. This allows controllers to power down more aggressively
> when there are no actively managed endpoints.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
> ---
>  drivers/pci/controller/pci-host-common.c | 47 ++++++++++++++++++++++++++++++++
>  drivers/pci/controller/pci-host-common.h |  2 ++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index d6258c1cffe5ec480fd2a7e50b3af39ef6ac4c8c..bff23bcdb5d032d2781d963eebe4a3fac0505517 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -106,5 +106,52 @@ void pci_host_common_remove(struct platform_device *pdev)
>  }
>  EXPORT_SYMBOL_GPL(pci_host_common_remove);
>  
> +static int __pci_host_common_d3cold_possible(struct pci_dev *pdev, void *userdata)
> +{
> +	bool *d3cold_possible = userdata;
> +
> +	if (pci_pcie_type(pdev) != PCI_EXP_TYPE_ENDPOINT)
> +		return 0;
> +
> +	if (!pdev->dev.driver && !pci_is_enabled(pdev))
> +		return 0;
> +
> +	if (pdev->current_state != PCI_D3hot)
> +		goto exit;
> +
> +	if (device_may_wakeup(&pdev->dev) && !pci_pme_capable(pdev, PCI_D3cold))
> +		goto exit;
> +
> +	return 0;
> +
> +exit:
> +	*d3cold_possible = false;
> +
> +	return -EOPNOTSUPP;
> +}
> +
> +/**
> + * pci_host_common_d3cold_possible - Determine whether a host bridge can enter D3cold

"Determine whether the host bridge can transition the devices into D3Cold"

- Mani

-- 
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