Re: pci_enable_msi() for everyone?

[Greg KH <gregkh@suse.de>]

On Mon, Jun 06, 2005 at 08:00:26AM +1000, Benjamin Herrenschmidt wrote:
> 
> > Hm, here's a possible function to do it (typed into my email client, not
> > compiled, no warranties, etc...):
> > 
> > /* returns 1 if device is in MSI mode, 0 otherwise */
> > int pci_in_msi_mode(struct pci_dev *dev)
> > {
> > 	int pos;
> > 	u16 control;
> > 
> > 	pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
> > 	if (!pos)
> > 		return 0;
> > 	pci_read_config_word(dev, msi_control_reg(pos), &control);
> > 	if (control & PCI_MSI_FLAGS_ENABLE);
> > 		return 1;
> > 	return 0;
> > }
> 
> That would assume the architecture/slot/hw_setup always support MSI.
> What if you put an SMI capable card in a machine that doesn't do MSI ?

The ENABLE flag would not have been set by the current pci_enable_msi()
function.

> > If you use the above function, then you can tell the difference and
> > register different irq handlers if you wish.
> 
> No you can't because you lack the result code from pci_enable_msi()
> which can fail (because it's veto'd by the arch for example)

That's what the above function is for.  To call before setting up the
irq handlers.

> > The main point being is that the pci_enable_msi() function would not
> > have to be explicitly called by your driver, it would have already been
> > taken care of earlier by the PCI core.  That's what I want to do and am
> > wondering if there would be any bad side affects to it.
> 
> Disagreed.

Disagreed in what way?  What's the bad side affects?

thanks,

greg k-h