linux-kernel - Re: [PATCH 01/30] staging: comedi: add pci_dev pointer to comedi

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Message-ID: <20120717020034.GA28771@kroah.com>
Date:	Mon, 16 Jul 2012 19:00:34 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
Cc:	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"abbotti@....co.uk" <abbotti@....co.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/30] staging: comedi: add pci_dev pointer to
 comedi_device

On Mon, Jul 16, 2012 at 08:55:47PM -0500, H Hartley Sweeten wrote:
> On Monday, July 16, 2012 6:52 PM, Greg KH wrote:
> > On Wed, Jul 11, 2012 at 02:49:14PM -0700, H Hartley Sweeten wrote:
> >> The pci_dev pointer in the private driver data is used by every
> >> comedi pci driver. Some of them only have the need for the
> >> private data because of this pointer.
> >> 
> >> Introduce the pci_dev pointer in the comedi_device struct so it
> >> can be used instead of needing it in the private data.
> >> 
> >> 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/comedidev.h | 2 ++
> >>  1 file changed, 2 insertions(+)
> >> 
> >> diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
> >> index de8c99c..55f2373 100644
> >> --- a/drivers/staging/comedi/comedidev.h
> >> +++ b/drivers/staging/comedi/comedidev.h
> >> @@ -212,6 +212,8 @@ struct comedi_device {
> >>  	 * DMA_NONE */
> >>  	struct device *hw_dev;
> >>  
> >> +	struct pci_dev *pcidev;
> >
> > No, the field above this, hw_dev, should be used instead here, as that's
> > what it is there for, right?
> 
> The hw_dev pointer is currently only used for something dealing with dma.
> I have not dug into it yet to see what exactly it's used for.  The comment
> says:
> 
> 	/* hw_dev is passed to dma_alloc_coherent when allocating async buffers
> 	 * for subdevices that have async_dma_dir set to something other than
> 	 * DMA_NONE */

Which is exactly what the pci device should be used for, it knows this
information :)

> > Care to rework this series with that change instead?
> 
> It could probably be used with some sort of container_of but I'm not sure.

Yes it can.

To set the field:

	hw_dev = &pci_dev->dev;

to get it back:
	pci_dev = container_of(hw_dev, struct pci_device, struct device);

I think.  That's off the top of my head, please try it out first.

And use a macro for the container_of stuff, that makes it easier to
understand.

thanks,

greg k-h
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