Subject: Re: [PATCH v2 6/9] PCI: Add pci_find_dvsec_capability to find designated VSEC

From: Jonathan Cameron <[email-masked]>
Date: Fri, 1 Oct 2021 10:42:26 +0100

On Thu, 23 Sep 2021 10:26:44 -0700
Ben Widawsky <[email-masked]> wrote:

> Add pci_find_dvsec_capability to locate a Designated Vendor-Specific
> Extended Capability with the specified DVSEC ID.
> 
> The Designated Vendor-Specific Extended Capability (DVSEC) allows one or
> more vendor specific capabilities that aren't tied to the vendor ID of
> the PCI component.
> 
> DVSEC is critical for both the Compute Express Link (CXL) driver as well
> as the driver for OpenCAPI coherent accelerator (OCXL).
> 
> Cc: David E. Box <[email-masked]>
> Cc: Jonathan Cameron <[email-masked]>
> Cc: Bjorn Helgaas <[email-masked]>
> Cc: Dan Williams <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Cc: Andrew Donnellan <[email-masked]>
> Cc: Lu Baolu <[email-masked]>
> Reviewed-by: Frederic Barrat <[email-masked]>
> Signed-off-by: Ben Widawsky <[email-masked]>

Great to see this cleaned up.

Reviewed-by: Jonathan Cameron <[email-masked]>

> ---
>  drivers/pci/pci.c   | 32 ++++++++++++++++++++++++++++++++
>  include/linux/pci.h |  1 +
>  2 files changed, 33 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index ce2ab62b64cf..94ac86ff28b0 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -732,6 +732,38 @@ u16 pci_find_vsec_capability(struct pci_dev *dev, u16 vendor, int cap)
>  }
>  EXPORT_SYMBOL_GPL(pci_find_vsec_capability);
>  
> +/**
> + * pci_find_dvsec_capability - Find DVSEC for vendor
> + * @dev: PCI device to query
> + * @vendor: Vendor ID to match for the DVSEC
> + * @dvsec: Designated Vendor-specific capability ID
> + *
> + * If DVSEC has Vendor ID @vendor and DVSEC ID @dvsec return the capability
> + * offset in config space; otherwise return 0.
> + */
> +u16 pci_find_dvsec_capability(struct pci_dev *dev, u16 vendor, u16 dvsec)
> +{
> +	int pos;
> +
> +	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DVSEC);
> +	if (!pos)
> +		return 0;
> +
> +	while (pos) {
> +		u16 v, id;
> +
> +		pci_read_config_word(dev, pos + PCI_DVSEC_HEADER1, &v);
> +		pci_read_config_word(dev, pos + PCI_DVSEC_HEADER2, &id);
> +		if (vendor == v && dvsec == id)
> +			return pos;
> +
> +		pos = pci_find_next_ext_capability(dev, pos, PCI_EXT_CAP_ID_DVSEC);
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(pci_find_dvsec_capability);
> +
>  /**
>   * pci_find_parent_resource - return resource region of parent bus of given
>   *			      region
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index cd8aa6fce204..c93ccfa4571b 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1130,6 +1130,7 @@ u16 pci_find_ext_capability(struct pci_dev *dev, int cap);
>  u16 pci_find_next_ext_capability(struct pci_dev *dev, u16 pos, int cap);
>  struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
>  u16 pci_find_vsec_capability(struct pci_dev *dev, u16 vendor, int cap);
> +u16 pci_find_dvsec_capability(struct pci_dev *dev, u16 vendor, u16 dvsec);
>  
>  u64 pci_get_dsn(struct pci_dev *dev);
>