[v1,1/4] PCI: Introduce pcim_alloc_irq_vectors()

Introduce pcim_alloc_irq_vectors(), a explicit device-managed version of
pci_alloc_irq_vectors().

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
---
 drivers/pci/pci.c   | 19 +++++++++++++++++++
 include/linux/pci.h |  3 +++
 2 files changed, 22 insertions(+)

Hi Dejin,

Thank you for all the work here!

The subject and the commit message could be improved to include a little
more details about why do you want to do it, and what problems does it
aims to solve.

> Introduce pcim_alloc_irq_vectors(), a explicit device-managed version of
> pci_alloc_irq_vectors().

You can probably drop the "explicit" word from the sentence above.
 
> +/**
> + * pcim_alloc_irq_vectors - a device-managed pci_alloc_irq_vectors()
> + *
> + * It depends on calling pcim_enable_device() to make irq resources manageable.
> + */

It would be "IRQ" in the sentence above.  Also see [1] for more details
about how to make a patch ready to be accepted.

Also, this comment looks like it's intended to be compliant with the
kernel-doc format, and if so, then you should describe each argument as
the bare minimum, so that the entire comment would become this function
documentation making it also a little more useful.  See [2] for an
example of how to use kernel-doc.

> +int pcim_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
> +				unsigned int max_vecs, unsigned int flags)
> +{
> +	struct pci_devres *dr;
> +
> +       /*Ensure that the pcim_enable_device() function has been called*/

The comment above has to be correctly aligned and it's also missing
spaces around the sentence to be properly formatted, see [3].

> +	dr = find_pci_dr(dev);
> +	if (!dr || !dr->enabled)
> +		return -EINVAL;
> +
> +	return pci_alloc_irq_vectors(dev, min_vecs, max_vecs, flags);
> +}

Question: wouldn't you need to call pci_free_irq_vectors() somewhere,
possibly to pcim_release() callback?  Although, I am not sure where the
right place would be.

I am asking, as the documentation (see [4]) suggests that one would have
to release allocated IRQ vectors (relevant exceprt):

>> To automatically use MSI or MSI-X interrupt vectors, use the following
>> function:
>>
>>  int pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
>>		unsigned int max_vecs, unsigned int flags);
>>
>> which allocates up to max_vecs interrupt vectors for a PCI device.
>>
>> (...)
>>
>> Any allocated resources should be freed before removing the device using
>> the following function:
>>
>>  void pci_free_irq_vectors(struct pci_dev *dev);

What do you think?

1. https://lore.kernel.org/linux-pci/20171026223701.GA25649@bhelgaas-glaptop.roam.corp.google.com/
2. https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html
3. https://www.kernel.org/doc/html/latest/process/coding-style.html
4. https://www.kernel.org/doc/html/latest/PCI/msi-howto.html

Krzysztof

On Mon, Feb 15, 2021 at 09:55:06PM +0100, Krzysztof Wilczyński wrote:

> Question: wouldn't you need to call pci_free_irq_vectors() somewhere,
> possibly to pcim_release() callback?  Although, I am not sure where the
> right place would be.
> 
> I am asking, as the documentation (see [4]) suggests that one would have
> to release allocated IRQ vectors (relevant exceprt):

It's done in pcim_release() but not explicitly.

        if (dev->msi_enabled)
                pci_disable_msi(dev);
        if (dev->msix_enabled)
                pci_disable_msix(dev);

Maybe above can be replaced by pci_free_irq_vectors() to be sure that any
future change to PCI IRQ allocation APIs.

Yes, I have checked and currently the above code is equivalent to
pci_free_irq_vectors().

Dejin, please update your patch accordingly.

On Tue, Feb 16, 2021 at 12:12:39PM +0200, Andy Shevchenko wrote:
> On Mon, Feb 15, 2021 at 09:55:06PM +0100, Krzysztof Wilczyński wrote:
> 
> > Question: wouldn't you need to call pci_free_irq_vectors() somewhere,
> > possibly to pcim_release() callback?  Although, I am not sure where the
> > right place would be.
> > 
> > I am asking, as the documentation (see [4]) suggests that one would have
> > to release allocated IRQ vectors (relevant exceprt):
> 
> It's done in pcim_release() but not explicitly.
> 
>         if (dev->msi_enabled)
>                 pci_disable_msi(dev);
>         if (dev->msix_enabled)
>                 pci_disable_msix(dev);
> 
> Maybe above can be replaced by pci_free_irq_vectors() to be sure that any
> future change to PCI IRQ allocation APIs.
> 
> Yes, I have checked and currently the above code is equivalent to
> pci_free_irq_vectors().
> 
> Dejin, please update your patch accordingly.
>
Hi Andy and Krzysztof,

I have modified it and sent patch v2. thank you very much!

BR,
Dejin

> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>

Hi Dejin and Andy,

[...]
> > > Question: wouldn't you need to call pci_free_irq_vectors() somewhere,
> > > possibly to pcim_release() callback?  Although, I am not sure where the
> > > right place would be.
> > > 
> > > I am asking, as the documentation (see [4]) suggests that one would have
> > > to release allocated IRQ vectors (relevant exceprt):
> > 
> > It's done in pcim_release() but not explicitly.
> > 
> >         if (dev->msi_enabled)
> >                 pci_disable_msi(dev);
> >         if (dev->msix_enabled)
> >                 pci_disable_msix(dev);
> > 
> > Maybe above can be replaced by pci_free_irq_vectors() to be sure that any
> > future change to PCI IRQ allocation APIs.
> > 
> > Yes, I have checked and currently the above code is equivalent to
> > pci_free_irq_vectors().
> > 
> > Dejin, please update your patch accordingly.
> >
> Hi Andy and Krzysztof,
> 
> I have modified it and sent patch v2. thank you very much!

Thank you Andy for double-checking!  Much appreciated.

Moving to pci_free_irq_vectors() directly looks great as we are also
removing the surplus checks that pcim_release() is doing - since both
the pci_disable_msi() and the pci_disable_msix() are doing internal
validation to see whether MSI/MSI-X is currently enabled.

Thank you again, Dejin and Andy. :)

Krzysztof