linux-kernel - Re: [PATCH RFC 07/77] PCI/MSI: Re-design MSI/MSI-X interrupts enablement pattern

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Message-ID: <20131008074826.GD10669@dhcp-26-207.brq.redhat.com>
Date:	Tue, 8 Oct 2013 09:48:26 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Michael Ellerman <michael@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Andy King <acking@...are.com>, Jon Mason <jon.mason@...el.com>,
	Matt Porter <mporter@...nel.crashing.org>,
	linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-mips@...ux-mips.org, linuxppc-dev@...ts.ozlabs.org,
	linux390@...ibm.com, linux-s390@...r.kernel.org, x86@...nel.org,
	linux-ide@...r.kernel.org, iss_storagedev@...com,
	linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net,
	linux-driver@...gic.com,
	Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
	"VMware, Inc." <pv-drivers@...are.com>, linux-scsi@...r.kernel.org
Subject: Re: [PATCH RFC 07/77] PCI/MSI: Re-design MSI/MSI-X interrupts
 enablement pattern

On Mon, Oct 07, 2013 at 02:17:49PM -0400, Tejun Heo wrote:
> Hello,
> 
> On Wed, Oct 02, 2013 at 12:48:23PM +0200, Alexander Gordeev wrote:
> > +static int foo_driver_enable_msi(struct foo_adapter *adapter, int nvec)
> > +{
> > +	rc = pci_get_msi_cap(adapter->pdev);
> > +	if (rc < 0)
> > +		return rc;
> > +
> > +	nvec = min(nvec, rc);
> > +	if (nvec < FOO_DRIVER_MINIMUM_NVEC) {
> > +		return -ENOSPC;
> > +
> > +	rc = pci_enable_msi_block(adapter->pdev, nvec);
> > +	return rc;
> > +}
> 
> If there are many which duplicate the above pattern, it'd probably be
> worthwhile to provide a helper?  It's usually a good idea to reduce
> the amount of boilerplate code in drivers.

I wanted to limit discussion in v1 to as little changes as possible.
I 'planned' those helper(s) for a separate effort if/when the most
important change is accepted and soaked a bit.

> > @@ -975,7 +951,7 @@ int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec)
> >  	if (nr_entries < 0)
> >  		return nr_entries;
> >  	if (nvec > nr_entries)
> > -		return nr_entries;
> > +		return -EINVAL;
> >  
> >  	/* Check for any invalid entries */
> >  	for (i = 0; i < nvec; i++) {
> 
> If we do things this way, it breaks all drivers using this interface
> until they're converted, right?

Right. And the rest of the series does it.

> Also, it probably isn't the best idea
> to flip the behavior like this as this can go completely unnoticed (no
> compiler warning or anything, the same function just behaves
> differently).  Maybe it'd be a better idea to introduce a simpler
> interface that most can be converted to?

Well, an *other* interface is a good idea. What do you mean with the
simpler here?

> tejun

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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