Re: [RFC PATCH v3 02/20] PCI/PM: Add a power-state helper that tries the bus lock

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Nov 12, 2026 at 02:16:14PM +0000, Shameer Kolothum wrote:
> PCI error recovery can hold pci_bus_sem for reading while waiting for a
> lock held by a driver. If that driver also needs the bus read lock to
> bring a device to D0, a queued writer can block it. Recovery, the driver
> and the writer then all wait for each other.
> 
> Add pci_try_set_power_state(), which returns -EAGAIN if it cannot take
> the bus lock immediately. The caller can then release its locks. Once
> the bus lock is held, use pci_set_power_state_locked() for the transition.
> Keep the existing cases that need no power-state change. The transition
> itself can still sleep.
> 
> Callers that already hold the bus read lock must use the locked helper
> instead.
> 
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  include/linux/pci.h |  3 +++
>  drivers/pci/pci.c   | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index aa3765a20a96..542fa4af0a43 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1535,6 +1535,7 @@ int pci_load_and_free_saved_state(struct pci_dev *dev,
>  int pci_platform_power_transition(struct pci_dev *dev, pci_power_t state);
>  int pci_set_power_state(struct pci_dev *dev, pci_power_t state);
>  int pci_set_power_state_locked(struct pci_dev *dev, pci_power_t state);
> +int pci_try_set_power_state(struct pci_dev *dev, pci_power_t state);
>  pci_power_t pci_choose_state(struct pci_dev *dev, pm_message_t state);
>  bool pci_pme_capable(struct pci_dev *dev, pci_power_t state);
>  void pci_pme_active(struct pci_dev *dev, bool enable);
> @@ -2216,6 +2217,8 @@ static inline int pci_set_power_state(struct pci_dev *dev, pci_power_t state)
>  { return 0; }
>  static inline int pci_set_power_state_locked(struct pci_dev *dev, pci_power_t state)
>  { return 0; }
> +static inline int pci_try_set_power_state(struct pci_dev *dev, pci_power_t state)
> +{ return 0; }
>  static inline int pci_wake_from_d3(struct pci_dev *dev, bool enable)
>  { return 0; }
>  static inline pci_power_t pci_choose_state(struct pci_dev *dev,
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7c6f2aba8144..f2ebd19204aa 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1655,6 +1655,43 @@ int pci_set_power_state_locked(struct pci_dev *dev, pci_power_t state)
>  }
>  EXPORT_SYMBOL(pci_set_power_state_locked);
>  
> +/**
> + * pci_try_set_power_state - Set power state without waiting for the bus lock
> + * @dev: PCI device to handle
> + * @state: Target PCI power state
> + *
> + * Like pci_set_power_state(), but return -EAGAIN without changing the power
> + * state if the bus lock cannot be acquired immediately. The transition
> + * itself can sleep.
> + *
> + * Callers already holding the bus read lock must use
> + * pci_set_power_state_locked().
> + */
> +int pci_try_set_power_state(struct pci_dev *dev, pci_power_t state)
> +{
> +	int ret;
> +
> +	if (state > PCI_D3cold)
> +		state = PCI_D3cold;
> +	else if (state < PCI_D0)
> +		state = PCI_D0;
> +	else if ((state == PCI_D1 || state == PCI_D2) && pci_no_d1d2(dev))
> +		return 0;
> +
> +	if (dev->current_state == state)
> +		return 0;
> +	if (state >= PCI_D3hot && (dev->dev_flags & PCI_DEV_FLAGS_NO_D3))
> +		return 0;
> +
> +	if (!down_read_trylock(&pci_bus_sem))
> +		return -EAGAIN;
> +	ret = pci_set_power_state_locked(dev, state);
> +	up_read(&pci_bus_sem);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(pci_try_set_power_state);
> +
>  #define PCI_EXP_SAVE_REGS	7
>  
>  static struct pci_cap_saved_state *_pci_find_saved_cap(struct pci_dev *pci_dev,
> -- 
> 2.43.0
>