linux-kernel - Re: [PATCH v2 02/11] PCI: Add the pci_get_class

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Message-ID: <19dc4b81-5b72-247c-d459-3ea9d1cddff0@linux.intel.com>
Date:   Wed, 9 Aug 2023 17:01:44 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Sui Jingfeng <sui.jingfeng@...ux.dev>
cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Dave Airlie <airlied@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-pci@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Sui Jingfeng <suijingfeng@...ngson.cn>
Subject: Re: [PATCH v2 02/11] PCI: Add the pci_get_class_masked() helper

On Wed, 9 Aug 2023, Sui Jingfeng wrote:

> From: Sui Jingfeng <suijingfeng@...ngson.cn>
> 
> Because there is no good way to get the mask member used to searching for
> devices that conform to a specific PCI class code, an application needs to
> process all PCI display devices can achieve its goal as follows:

This is mixing old and new way in a single sentence (which is confusing)?
 
> pdev = NULL;
> do {
> 	pdev = pci_get_class_masked(PCI_BASE_CLASS_DISPLAY << 16, 0xFF0000, pdev);
> 	if (pdev)
> 		do_something_for_pci_display_device(pdev);
> } while (pdev);
> 
> While previously, we just can not ignore Sub-Class code and the Programming

cannot

> Interface byte when do the searching.

doing the search.

> 
> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
> ---
>  drivers/pci/search.c | 30 ++++++++++++++++++++++++++++++
>  include/linux/pci.h  |  7 +++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> index b4c138a6ec02..f1c15aea868b 100644
> --- a/drivers/pci/search.c
> +++ b/drivers/pci/search.c
> @@ -334,6 +334,36 @@ struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
>  }
>  EXPORT_SYMBOL(pci_get_device);
>  
> +/**
> + * pci_get_class_masked - begin or continue searching for a PCI device by class and mask
> + * @class: search for a PCI device with this class designation
> + * @from: Previous PCI device found in search, or %NULL for new search.
> + *
> + * Iterates through the list of known PCI devices.  If a PCI device is

No double spaces in kernel comments. Perhaps your editor might be adding 
them on reflow (might be configurable to not do that).

> + * found with a matching @class, the reference count to the device is
> + * incremented and a pointer to its device structure is returned.
> + * Otherwise, %NULL is returned.
> + * A new search is initiated by passing %NULL as the @from argument.
> + * Otherwise if @from is not %NULL, searches continue from next device
> + * on the global list.  The reference count for @from is always decremented
> + * if it is not %NULL.

Use kerneldoc's Return: section for describing return value.

> + */
> +struct pci_dev *pci_get_class_masked(unsigned int class, unsigned int mask,
> +				     struct pci_dev *from)
> +{
> +	struct pci_device_id id = {
> +		.vendor = PCI_ANY_ID,
> +		.device = PCI_ANY_ID,
> +		.subvendor = PCI_ANY_ID,
> +		.subdevice = PCI_ANY_ID,
> +		.class_mask = mask,
> +		.class = class,
> +	};
> +
> +	return pci_get_dev_by_id(&id, from);
> +}
> +EXPORT_SYMBOL(pci_get_class_masked);
> +
>  /**
>   * pci_get_class - begin or continue searching for a PCI device by class
>   * @class: search for a PCI device with this class designation
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 0ff7500772e6..b20e7ba844bf 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1180,6 +1180,9 @@ struct pci_dev *pci_get_slot(struct pci_bus *bus, unsigned int devfn);
>  struct pci_dev *pci_get_domain_bus_and_slot(int domain, unsigned int bus,
>  					    unsigned int devfn);
>  struct pci_dev *pci_get_class(unsigned int class, struct pci_dev *from);
> +struct pci_dev *pci_get_class_masked(unsigned int class, unsigned int mask,
> +				     struct pci_dev *from);
> +
>  int pci_dev_present(const struct pci_device_id *ids);
>  
>  int pci_bus_read_config_byte(struct pci_bus *bus, unsigned int devfn,
> @@ -1895,6 +1898,10 @@ static inline struct pci_dev *pci_get_class(unsigned int class,
>  					    struct pci_dev *from)
>  { return NULL; }
>  
> +static inline struct pci_dev *pci_get_class_masked(unsigned int class,
> +						   unsigned int mask,
> +						   struct pci_dev *from)
> +{ return NULL; }
>  
>  static inline int pci_dev_present(const struct pci_device_id *ids)
>  { return 0; }
> 

-- 
 i.