linux-kernel - RE: [PATCH 15/90] staging: comedi: adv_pci1723: move comedi_pci

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Date:	Thu, 19 Jul 2012 12:12:02 -0500
From:	H Hartley Sweeten <hartleys@...ionengravers.com>
To:	Ian Abbott <abbotti@....co.uk>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	Ian Abbott <ian.abbott@....co.uk>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: RE: [PATCH 15/90] staging: comedi: adv_pci1723: move
 comedi_pci_enable() into the attach

On Thursday, July 19, 2012 2:38 AM, Ian Abbott wrote:
> On 2012-07-19 02:30, H Hartley Sweeten wrote:
>> Use pci_is_enabled() in the "find pci device" function to determine if
>> the found pci device is not in use and move the comedi_pci_enable() call
>> into the attach.
>>
>> Signed-off-by: H Hartley Sweeten <hsweeten@...ionengravers.com>
>> Cc: Ian Abbott <abbotti@....co.uk>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> ---
>>   drivers/staging/comedi/drivers/adv_pci1723.c | 10 +++++-----
>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/staging/comedi/drivers/adv_pci1723.c b/drivers/staging/comedi/drivers/adv_pci1723.c
>> index f561a2a..e971fa6 100644
>> --- a/drivers/staging/comedi/drivers/adv_pci1723.c
>> +++ b/drivers/staging/comedi/drivers/adv_pci1723.c
>> @@ -302,11 +302,7 @@ static struct pci_dev *pci1723_find_pci_dev(struct comedi_device *dev,
>>   		}
>>   		if (pcidev->vendor != PCI_VENDOR_ID_ADVANTECH)
>>   			continue;
>> -		/*
>> -		 * Look for device that isn't in use.
>> -		 * Enable PCI device and request regions.
>> -		 */
>> -		if (comedi_pci_enable(pcidev, "adv_pci1723"))
>> +		if (pci_is_enabled(pcidev))
>>   			continue;
>>   		return pcidev;
>>   	}
>
> Just because the device is enabled doesn't mean that it is in use, so 
> this change could skip over a perfectly good unused device.

Are you sure? According to Documentation/PCI/pci.txt, the first thing
a driver "should" do when taking ownership of a PCI device is enable
the device. The last thing it "should" do when being unloaded is
disable the device.

It would seem that checking pci_is_enabled() would let us know that
the pci_dev in question is being used.

> If you want to move the comedi_pci_enable() call, this is a change in 
> behaviour for this particular driver, but is consistent with most of the 
> other Comedi PCI drivers (and the bus/slot options can be used to select 
> a particular device).  This is probably a good thing, but you should 
> take out the pci_is_enabled test.

I was curious about this.

In the original driver, doing an 'attach' with bus/slot both = 0 would result
in the pci bus being walked to find the first device that could be enabled
(i.e. a "free" device) and using that device. This allows doing the 'attach'
with more than one card installed and being able to attach to each one
by simply:

comedi_config /dev/comedi0 adv_pci1723
comedi_config /dev/comedi1 adv_pci1723
etc.

The "normal" operation for the comedi pci drivers appears to require
the bus/slot information when multiple devices are used. Or implement
the 'attach_pci' callback in the comedi_driver and allow the core to
simply pass the pci_dev directly to the driver.

What would you prefer?

I was planning on making a comedi_find_pci_dev() function that the
drivers could call with a "match" callback. This would allow a common
function for most of the boilerplate code and just require the drivers
to check the the match against the boardinfo dev/id, etc. as required.
Something like:

struct pci_dev *comedi_find_pci_dev(struct comedi_device *dev,
	struct comedi_devconfig *it,
	const void *(*match)(struct comedi_device *,
				struct pci_dev *))
{
	struct pci_dev *pcidev = NULL;
	int bus = it->options[0];
	int slot = it->options[1];

	for_each_pci_dev(pcidev) {
		/* pci_is_enabled() test? */
		if ((bus && bus != pcidev->bus->number) ||
		    (slot && slot != PCI_SLOT(pcidev->devfn)))
			continue;
		dev->board_ptr = match(dev, pcidev);
		if (dev->board_ptr) {
			comedi_set_hw_dev(dev, &pcidev->dev);
			return pcidev;
		}
	}
	return NULL;
}

The "match" function for a driver would then just be something like:

const void *match_pci(struct comedi_device *dev, struct pci_dev *pcidev)
{
	const struct boardinfo *board;
	int i;

	for (i = 0; i < ARRAY_SIZE(boardinfo); i++) {
		board = &boardinfo[i];
		if (pcidev->vendor != board->ven_id ||
		    pcidev->device != board->dev_id)
			continue;
		return board;
	}
	return NULL;
}

This would require adding a dummy boardinfo to some of the drivers but
I think it's cleaner.

Comments?

Regards,
Hartley