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

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Message-ID: <9e512f44-c47f-85e8-0ea-81d7cbc99a67@linux.intel.com>
Date:   Fri, 11 Aug 2023 09:31:15 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     suijingfeng <suijingfeng@...ngson.cn>
cc:     Sui Jingfeng <sui.jingfeng@...ux.dev>,
        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,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 02/11] PCI: Add the pci_get_class_masked() helper

On Thu, 10 Aug 2023, suijingfeng wrote:

> Hi,
> 
> 
> On 2023/8/9 22:01, Ilpo Järvinen wrote:
> > 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)?
> 
> 
> Thanks for reviewing, but I can't understand this sentence.
> Are you telling me that my description have grammar problem or something else?

I think it's a bit of both.

> I means that before apply this patch, we don't have a function can be used
> to get all PCI(e) devices in a system by matching against its the PCI base
> class code only,
> while keep the Sub-Class code and the Programming Interface ignored.
> By supply a mask as argument, such thing become possible.

This explanation you put into this reply is much easier to follow and 
understand. I recommend you'd use it to replace the unclear fragment 
above. So something along the lines of:

  There is no function that can be used to get all PCI(e) devices in a 
  system by matching against its the PCI base class code only, while keep 
  the Sub-Class code and the Programming Interface ignored.

  Add pci_get_class_masked() to allow supplying a mask for the get.

  [After this you can put the explanining code block+its intro if you 
   want]

-- 
 i.

> If an application want to process all PCI display devices in the system,
> then it can achieve its goal by calling pci_get_class_masked() function.
> 
> 
> > > 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.
> 
> 
> OK, will be fixed at the next version.
> 
> 
> > > 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; }
> > > 
>