Re: [PATCH 1/4] PCI: Introduce an API to check if RC/platform can retain device context during suspend

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Rafael]

On Tue, Apr 14, 2026 at 09:29:39PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> From: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
> 
> Currently, the PCI endpoint drivers like NVMe checks whether the device
> context will be retained or not during system suspend, with the help of
> pm_suspend_via_firmware() API.
> 
> But it is possible that the device context might be lost due to some
> platform limitation as well. Having those checks in the endpoint drivers
> will not scale and will cause a lot of code duplication.
> 
> So introduce an API that acts as a sole point of truth that the endpoint
> drivers can rely on to check whether they can expect the device context
> to be retained or not.
> 
> If the API returns 'false', then the client drivers need to prepare for
> context loss by performing actions such as resetting the device, saving
> the context, shutting it down etc... If it returns 'true', then the drivers
> do not need to perform any special action and can leave the device in
> active state.
> 
> Right now, this API only incorporates the pm_suspend_via_firmware() check.
> But will be extended in the future commits.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
> ---
>  drivers/pci/pci.c   | 23 +++++++++++++++++++++++
>  include/linux/pci.h |  7 +++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 8479c2e1f74f..211616467a77 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -33,6 +33,7 @@
>  #include <asm/dma.h>
>  #include <linux/aer.h>
>  #include <linux/bitfield.h>
> +#include <linux/suspend.h>
>  #include "pci.h"
>  
>  DEFINE_MUTEX(pci_slot_mutex);
> @@ -2900,6 +2901,28 @@ void pci_config_pm_runtime_put(struct pci_dev *pdev)
>  		pm_runtime_put_sync(parent);
>  }
>  
> +/**
> + * pci_dev_suspend_retention_supported - Check if the platform can retain the device
> + *					 context during system suspend
> + * @pdev: PCI device to check
> + *
> + * Returns true if the platform can guarantee to retain the device context,
> + * false otherwise.
> + */
> +bool pci_dev_suspend_retention_supported(struct pci_dev *pdev)

This doesn't seem like the right name.  This isn't a property of the
*device*; that's all determined by the PCI spec (devices must retain
all internal state in D0, D1, and D2, they retain it in D3hot if
No_Soft_Reset, and they never do in D3cold).

So this seems like something to do with the *platform* behavior.  It
sounds like this is basically a way to learn whether the device might
be put in D3cold on system suspend.

> +{
> +	/*
> +	 * If the platform firmware (like ACPI) is involved at the end of system
> +	 * suspend, device context may not be retained.
> +	 */
> +	if (pm_suspend_via_firmware())
> +		return false;
> +
> +	/* Assume that the context is retained by default */
> +	return true;
> +}
> +EXPORT_SYMBOL_GPL(pci_dev_suspend_retention_supported);
> +
>  static const struct dmi_system_id bridge_d3_blacklist[] = {
>  #ifdef CONFIG_X86
>  	{
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 1c270f1d5123..d9bc7ad4eaa4 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2080,6 +2080,8 @@ pci_release_mem_regions(struct pci_dev *pdev)
>  			    pci_select_bars(pdev, IORESOURCE_MEM));
>  }
>  
> +bool pci_dev_suspend_retention_supported(struct pci_dev *pdev);
> +
>  #else /* CONFIG_PCI is not enabled */
>  
>  static inline void pci_set_flags(int flags) { }
> @@ -2239,6 +2241,11 @@ pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
>  static inline void pci_free_irq_vectors(struct pci_dev *dev)
>  {
>  }
> +
> +static inline bool pci_dev_suspend_retention_supported(struct pci_dev *pdev)
> +{
> +	return true;
> +}
>  #endif /* CONFIG_PCI */
>  
>  /* Include architecture-dependent settings and functions */
> 
> -- 
> 2.51.0
> 
>