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

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Message-ID: <20120719233506.GA12858@kroah.com>
Date:	Thu, 19 Jul 2012 16:35:06 -0700
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
Cc:	Ian Abbott <abbotti@....co.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	Ian Abbott <ian.abbott@....co.uk>
Subject: Re: [PATCH 15/90] staging: comedi: adv_pci1723: move
 comedi_pci_enable() into the attach

On Thu, Jul 19, 2012 at 06:31:23PM -0500, H Hartley Sweeten wrote:
> On Thursday, July 19, 2012 4:17 PM, gregkh wrote:
> > On Thu, Jul 19, 2012 at 12:12:02PM -0500, H Hartley Sweeten wrote:
> >> 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?
> >
> > Ick.  What ever happened to converting these drivers to use the PCI api
> > correctly and not to search the PCI space for the device, but have the
> > PCI core call them if the device is found?
> >
> > It looks like most of these drivers have already been converted to that
> > style, so these checks for "do we find a device" can all be removed
> > entirely now, right?  There's no way the functions would be called if
> > the device wasn't found in the first place.
> > 
> > Or am I missing something here?
> 
> If the comedi pci drivers have the "attach_pci" callback defined, the
> PCI api does correctly probe the driver. The comedi_pci_auto_config()
> then passes the pci_dev directly to the driver and the search of the
> PCI space for the device is not required.
> 
> If the "attach_pci" callback is not defined, the comedi_pci_auto_config()
> then falls back to passing the bus/slot information to the driver and uses
> the "attach" callback. In this case we could probably fast-track the search
> by using pci_get_slot() instead of doing the for_each_pci_dev() loop.
> 
> I think the problem is the COMEDI_DEVCONFIG ioctl. The userspace
> utility 'comedi_config' uses that ioctl to link a device node to a
> comedi driver. That utility allows passing the bus/slot information
> but it's not required. This means we have to search the PCI space
> for the pci_dev that matches the driver.

The ioctl shouldn't be needed anymore for PCI or USB devices, as the
kernel handles the matching of the driver to the device.  Even if it
didn't, there are other more "standard" ways that you can bind devices
to drivers (through sysfs.)

So, I'd really recommend ripping all of this logic out for PCI drivers
as odds are, it's not used, and probably doesn't really work.

For old ISA cards, it makes sense, but the odds that anyone uses any ISA
devices is pretty slim.

thanks,

greg k-h
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