Re: [RFC PATCH 01/13] PCI: Prepare removing devres from pci_intx()

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Fri, Oct 11, 2024 at 02:16:06PM +0200, Philipp Stanner wrote:
> On Thu, 2024-10-10 at 17:40 +0300, Andy Shevchenko wrote:
> > On Wed, Oct 09, 2024 at 10:35:07AM +0200, Philipp Stanner wrote:
> > > pci_intx() is a hybrid function which sometimes performs devres
> > > operations, depending on whether pcim_enable_device() has been used
> > > to
> > > enable the pci_dev. This sometimes-managed nature of the function
> > > is
> > > problematic. Notably, it causes the function to allocate under some
> > > circumstances which makes it unusable from interrupt context.
> > > 
> > > To, ultimately, remove the hybrid nature from pci_intx(), it is
> > > first
> > > necessary to provide an always-managed and a never-managed version
> > > of that function. Then, all callers of pci_intx() can be ported to
> > > the
> > > version they need, depending whether they use pci_enable_device()
> > > or
> > > pcim_enable_device().

> > > An always-managed function exists, namely pcim_intx(), for which
> > > __pcim_intx(), a never-managed version of pci_intx() had been
> > > implemented.
> > 
> > > Make __pcim_intx() a public function under the name
> > > pci_intx_unmanaged(). Make pcim_intx() a public function.

It seems I got confused by these two paragraphs. Why the double underscored
function is even mentioned here?

> > To avoid an additional churn we can make just completely new APIs,
> > namely:
> > pcim_int_x()
> > pci_int_x()
> > 
> > You won't need all dirty dances with double underscored function
> > naming and
> > renaming.
> 
> Ähm.. I can't follow. The new version doesn't use double underscores
> anymore. __pcim_intx() is being removed, effectively.
> After this series, we'd end up with a clean:
> 
>       pci_intx() <-> pcim_intx()
> 
> just as in the other PCI APIs.

...

> > > + pci_read_config_word(pdev, PCI_COMMAND, &pci_command);
> > > +
> > > + if (enable)
> > > +         new = pci_command & ~PCI_COMMAND_INTX_DISABLE;
> > > + else
> > > +         new = pci_command | PCI_COMMAND_INTX_DISABLE;
> > > +
> > > + if (new != pci_command)
> > 
> > I would use positive conditionals as easy to read (yes, a couple of
> > lines
> > longer, but also a win is the indentation and avoiding an additional
> > churn in
> > the future in case we need to add something in this branch.
> 
> I can't follow. You mean:
> 
> if (new == pci_command)
>     return;
> 
> ?
> 
> That's exactly the same level of indentation.

No, the body gets one level off.

> Plus, I just copied the code.
> 
> > > +         pci_write_config_word(pdev, PCI_COMMAND, new);

        if (new == pci_command)
                return;

        pci_write_config_word(pdev, PCI_COMMAND, new);

See the difference?
Also, imaging adding a new code in your case:

        if (new != pci_command)
                pci_write_config_word(pdev, PCI_COMMAND, new);

==>

        if (new != pci_command) {
                ...foo...
                pci_write_config_word(pdev, PCI_COMMAND, new);
                ...bar...
        }

And in mine:

        if (new == pci_command)
                return;

        ...foo...
        pci_write_config_word(pdev, PCI_COMMAND, new);
        ...bar...

I hope it's clear now what I meant.

-- 
With Best Regards,
Andy Shevchenko