linux-kernel - Re: [PATCH 2/2] PCI: Cache offset of Resizable BAR capability

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Message-ID: <75bb62bd-7944-1d74-ad84-fd676c8bfb91@linux.intel.com>
Date: Thu, 13 Feb 2025 15:54:39 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>
cc: Alex Williamson <alex.williamson@...hat.com>, 
    Christian König <ckoenig.leichtzumerken@...il.com>, 
    linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, 
    Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 2/2] PCI: Cache offset of Resizable BAR capability

On Fri, 7 Feb 2025, Bjorn Helgaas wrote:

> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> Previously most resizable BAR interfaces (pci_rebar_get_possible_sizes(),
> pci_rebar_set_size(), etc) as well as pci_restore_state() searched config
> space for a Resizable BAR capability.  Most devices don't have such a
> capability, so this is wasted effort, especially for pci_restore_state().
> 
> Search for a Resizable BAR capability once at enumeration-time and cache
> the offset so we don't have to search every time we need it.  No functional
> change intended.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/pci.c   | 9 +++++++--
>  drivers/pci/pci.h   | 1 +
>  drivers/pci/probe.c | 1 +
>  include/linux/pci.h | 1 +
>  4 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 503376bf7e75..cf2632080a94 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1872,7 +1872,7 @@ static void pci_restore_rebar_state(struct pci_dev *pdev)
>  	unsigned int pos, nbars, i;
>  	u32 ctrl;
>  
> -	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_REBAR);
> +	pos = pdev->rebar_cap;
>  	if (!pos)
>  		return;
>  
> @@ -3719,6 +3719,11 @@ void pci_acs_init(struct pci_dev *dev)
>  	pci_enable_acs(dev);
>  }
>  
> +void pci_rebar_init(struct pci_dev *pdev)
> +{
> +	pdev->rebar_cap = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_REBAR);
> +}
> +
>  /**
>   * pci_rebar_find_pos - find position of resize ctrl reg for BAR
>   * @pdev: PCI device
> @@ -3733,7 +3738,7 @@ static int pci_rebar_find_pos(struct pci_dev *pdev, int bar)
>  	unsigned int pos, nbars, i;
>  	u32 ctrl;
>  
> -	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_REBAR);
> +	pos = pdev->rebar_cap;
>  	if (!pos)
>  		return -ENOTSUPP;
>  
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 01e51db8d285..d7b46ddfd6d2 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -799,6 +799,7 @@ static inline int acpi_get_rc_resources(struct device *dev, const char *hid,
>  }
>  #endif
>  
> +void pci_rebar_init(struct pci_dev *pdev);
>  int pci_rebar_get_current_size(struct pci_dev *pdev, int bar);
>  int pci_rebar_set_size(struct pci_dev *pdev, int bar, int size);
>  static inline u64 pci_rebar_size_to_bytes(int size)
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index b6536ed599c3..24dd3dcfd223 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2564,6 +2564,7 @@ static void pci_init_capabilities(struct pci_dev *dev)
>  	pci_rcec_init(dev);		/* Root Complex Event Collector */
>  	pci_doe_init(dev);		/* Data Object Exchange */
>  	pci_tph_init(dev);		/* TLP Processing Hints */
> +	pci_rebar_init(dev);		/* Resizable BAR */
>  
>  	pcie_report_downtraining(dev);
>  	pci_init_reset_methods(dev);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 47b31ad724fa..9e5bbd996c83 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -353,6 +353,7 @@ struct pci_dev {
>  	struct pci_dev  *rcec;          /* Associated RCEC device */
>  #endif
>  	u32		devcap;		/* PCIe Device Capabilities */
> +	u16		rebar_cap;	/* Resizable BAR capability offset */
>  	u8		pcie_cap;	/* PCIe capability offset */
>  	u8		msi_cap;	/* MSI capability offset */
>  	u8		msix_cap;	/* MSI-X capability offset */

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.