Re: [PATCH 0/4] PCI: Introduce pci_dev_suspend_retention_supported() API

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Rafael]

On Tue, Apr 14, 2026 at 09:29:38PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> This series introduces a new PCI API
> pci_dev_suspend_retention_supported() to let the client drivers know
> whether they can expect context retention across suspend/resume or
> not and uses it in the NVMe PCI host driver.
> 
> This new API is targeted to abstract the PCI power management
> details away from the client drivers. This is needed because client
> drivers like NVMe make use of APIs such as pm_suspend_via_firmware()
> and decide to keep the device in low power mode if this API returns
> 'false'. But some platforms may have other limitations like in the
> case of Qcom, where if the RC driver removes the resource vote to
> allow the SoC to enter low power mode, it cannot reliably exit the
> L1ss state when the endpoint asserts CLKREQ#. So in this case also,
> the client drivers cannot keep the device in low power state during
> suspend and expect context retention.

I don't know what pm_suspend_via_firmware() means.  The kernel-doc
says "platform firmware is going to be invoked at the end of the
system-wide power management transition," but that doesn't say
anything about what firmware might do or what it means to drivers.

Based on d916b1be94b6 ("nvme-pci: use host managed power state for
suspend"), which used it in nvme_suspend(), I guess the assumption is
that pm_suspend_via_firmware() means the device might be put in D3cold
and lose all its internal state, and conversely,
!pm_suspend_via_firmware() means the device will *never* be put in a
low-power state that loses internal state.

> And these limitations may just keep adding in the future. Without a
> unified API, the client drivers have to implement their own logic
> which may cause code duplication and may also lead to drivers
> missing some of the platform limitations.
> 
> Once this series gets merged, we can extend this API usage to other
> client drivers as well.

> 
> Testing
> =======
> 
> This series is tested on Qualcomm Hamoa based Lenovo Thinkpad T14s latop with
> NVMe drive.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
> ---
> Manivannan Sadhasivam (4):
>       PCI: Introduce an API to check if RC/platform can retain device context during suspend
>       PCI: Indicate context lost if L1ss exit is broken during resume from system suspend
>       PCI: qcom: Indicate broken L1ss exit during resume from system suspend
>       nvme-pci: Use pci_dev_suspend_retention_supported() API during suspend
> 
>  drivers/nvme/host/pci.c                |  3 ++-
>  drivers/pci/controller/dwc/pcie-qcom.c | 11 +++++++++++
>  drivers/pci/pci.c                      | 34 ++++++++++++++++++++++++++++++++++
>  include/linux/pci.h                    |  9 +++++++++
>  4 files changed, 56 insertions(+), 1 deletion(-)
> ---
> base-commit: 591cd656a1bf5ea94a222af5ef2ee76df029c1d2
> change-id: 20260414-l1ss-fix-6c9cf2451944
> 
> Best regards,
> --  
> Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
> 
>