[3/7] ahci: Use new interfaces for MSI/MSI-X enablement

On Mon, Jan 13, 2014 at 12:12:20PM -0700, Bjorn Helgaas wrote:
> > -	nvec = rc;
> > -	rc = pci_enable_msi_block(pdev, nvec);
> > -	if (rc)
> > +	if (pci_enable_msi_range(pdev, nvec, nvec) < 0)
> >  		goto intx;
> >  
> >  	return nvec;
> >  
> >  single_msi:
> > -	rc = pci_enable_msi(pdev);
> > -	if (rc)
> > +	if (pci_enable_msi_range(pdev, 1, 1) < 0)
> 
> This part doesn't seem like an improvement.  There are a hundred or so
> callers of pci_enable_msi() that only want a single MSI.  Is there any
> benefit in changing them to use pci_enable_msi_range()?

In this particular case it reads better to me as one sees on the screen
pci_enable_msi_range(pdev, nvec, nvec) and pci_enable_msi_range(pdev, 1, 1)
calls. That allows to avoid switching in mind between negative-or-positive
return in the former call and negative-or-zero return from pci_enable_msi()
if we had it.

But in most cases when single MSI is enabled we do cause complication
with the patterns below (which I expect I am going be hated for ;) ):


-	rc = pci_enable_msi(pdev);
-	if (rc)
+	rc = pci_enable_msi_range(pdev, 1, 1);
+	if (rc < 0)
		...


-	rc = pci_enable_msi(pdev);
-	if (!rc)
+	rc = pci_enable_msi_range(pdev, 1, 1);
+	if (rc > 0)
		...

 
I think we have a tradeoff between the interface simplicity and code clarity.
What if we try to address both goals by making pci_enable_msi() a helper over
pci_enable_msi_range(pdev, 1, 1)? In this case the return value will match
negative-or-positive binary semantics while reads almost as good as it used to:


-	rc = pci_enable_msi(pdev);
-	if (rc)
+	rc = pci_enable_msi(pdev);
+	if (rc < 0)
		...


-	rc = pci_enable_msi(pdev);
-	if (!rc)
+	rc = pci_enable_msi(pdev);
+	if (rc > 0)
		...


The whole interface would not be inflated as well, with just:

On Tue, Jan 14, 2014 at 09:50:40AM +0100, Alexander Gordeev wrote:
> What if we try to address both goals by making pci_enable_msi() a helper over
> pci_enable_msi_range(pdev, 1, 1)?

Or pci_enable_msi_single() to help reading and avoid drivers conversion mess.

On Tue, Jan 14, 2014 at 1:50 AM, Alexander Gordeev <agordeev@redhat.com> wrote:
> On Mon, Jan 13, 2014 at 12:12:20PM -0700, Bjorn Helgaas wrote:
>> > -   nvec = rc;
>> > -   rc = pci_enable_msi_block(pdev, nvec);
>> > -   if (rc)
>> > +   if (pci_enable_msi_range(pdev, nvec, nvec) < 0)
>> >             goto intx;
>> >
>> >     return nvec;
>> >
>> >  single_msi:
>> > -   rc = pci_enable_msi(pdev);
>> > -   if (rc)
>> > +   if (pci_enable_msi_range(pdev, 1, 1) < 0)
>>
>> This part doesn't seem like an improvement.  There are a hundred or so
>> callers of pci_enable_msi() that only want a single MSI.  Is there any
>> benefit in changing them to use pci_enable_msi_range()?
>
> In this particular case it reads better to me as one sees on the screen
> pci_enable_msi_range(pdev, nvec, nvec) and pci_enable_msi_range(pdev, 1, 1)
> calls. That allows to avoid switching in mind between negative-or-positive
> return in the former call and negative-or-zero return from pci_enable_msi()
> if we had it.
>
> But in most cases when single MSI is enabled we do cause complication
> with the patterns below (which I expect I am going be hated for ;) ):

I don't want to touch those hundred pci_enable_msi() callers at all.
So I think we should have something like this:

    /* Return 0 for success (one MSI enabled) or negative errno */
    static inline int pci_enable_msi(struct pci_dev *dev)
    {
        int rc;

        rc = pci_enable_msi_range(pdev, 1, 1);
        if (rc == 1)
            return 0;
        return rc;
    }
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