Re: [PATCH 1/2] PCI: Add pci_find_next_dvsec_capability to find next designated VSEC

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc David since drivers/platform/x86/intel/vsec.c does some similar
things, although it seems to iterate over all Intel DVSEC IDs at once]

In subject:

  PCI: Add pci_find_next_dvsec_capability() to find next Designated VSEC

On Mon, Aug 07, 2023 at 11:18:45AM +0800, Xiongfeng Wang wrote:
> Some devices may have several DVSEC(Designated Vendor-Specific Extended
> Capability) entries with the same DVSEC ID. Add
> pci_find_next_dvsec_capability() to find them all.

Add space between "DVSEC" and "(Designated ...)".

> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>

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

so you can merge this along with the ocxl patch that uses it.

> ---
>  drivers/pci/pci.c   | 37 +++++++++++++++++++++++++------------
>  include/linux/pci.h |  2 ++
>  2 files changed, 27 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 60230da957e0..3455ca7306ae 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -749,35 +749,48 @@ 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
> + * pci_find_next_dvsec_capability - Find next DVSEC for vendor
>   * @dev: PCI device to query
> + * @start: address at which to start looking (0 to start at beginning of list)

s/address/Address/ to match other parameters

>   * @vendor: Vendor ID to match for the DVSEC
>   * @dvsec: Designated Vendor-specific capability ID

There are a lot of IDs floating around here, so to better match the
spec language:

  @dvsec: Vendor-defined DVSEC ID

> - * If DVSEC has Vendor ID @vendor and DVSEC ID @dvsec return the capability
> - * offset in config space; otherwise return 0.
> + * Returns the address of the next DVSEC if the DVSEC has Vendor ID @vendor and
> + * DVSEC ID @dvsec; otherwise return 0. DVSEC can occur several times with the
> + * same DVSEC ID for some devices, and this provides a way to find them all.
>   */
> -u16 pci_find_dvsec_capability(struct pci_dev *dev, u16 vendor, u16 dvsec)
> +u16 pci_find_next_dvsec_capability(struct pci_dev *dev, u16 start, u16 vendor,
> +				   u16 dvsec)
>  {
> -	int pos;
> +	u16 pos = start;
>  
> -	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DVSEC);
> -	if (!pos)
> -		return 0;
> -
> -	while (pos) {
> +	while ((pos = pci_find_next_ext_capability(dev, pos,
> +						  PCI_EXT_CAP_ID_DVSEC))) {
>  		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_next_dvsec_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)
> +{
> +	return pci_find_next_dvsec_capability(dev, 0, vendor, dvsec);
> +}
>  EXPORT_SYMBOL_GPL(pci_find_dvsec_capability);
>  
>  /**
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index c69a2cc1f412..82bb905daf72 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1168,6 +1168,8 @@ 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);
> +u16 pci_find_next_dvsec_capability(struct pci_dev *dev, u16 start, u16 vendor,
> +				   u16 dvsec);
>  
>  u64 pci_get_dsn(struct pci_dev *dev);
>  
> -- 
> 2.20.1
>