Subject: Re: [PATCH net-next v3 2/3] net: stmmac: Add glue driver for Motorcomm YT6801 ethernet controller

From: Yao Zi <[email-masked]>
Date: Thu, 11 Dec 2025 14:23:58 +0000

On Mon, Dec 08, 2025 at 10:54:36AM +0100, Philipp Stanner wrote:
> On Fri, 2025-12-05 at 16:16 -0600, Bjorn Helgaas wrote:
> > [+to Philipp, Thomas for MSI devres question]
> > 
> > On Fri, Dec 05, 2025 at 09:34:54AM +0000, Russell King (Oracle) wrote:
> > > On Fri, Dec 05, 2025 at 05:31:34AM +0000, Yao Zi wrote:
> > > > On Mon, Nov 24, 2025 at 07:06:12PM +0000, Russell King (Oracle) wrote:
> > > > > On Mon, Nov 24, 2025 at 04:32:10PM +0000, Yao Zi wrote:

...

> > > This looks very non-intuitive, and the documentation for
> > > pci_alloc_irq_vectors() doesn't help:
> > > 
> > >  * Upon a successful allocation, the caller should use pci_irq_vector()
> > >  * to get the Linux IRQ number to be passed to request_threaded_irq().
> > >  * The driver must call pci_free_irq_vectors() on cleanup.
> > >    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > 
> > > because if what you say is correct (and it looks like it is) then this
> > > line is blatently incorrect.
> 
> True, this line is false. It should probably state "If you didn't
> enable your PCI device with pcim_enable_device(), you must call
> pci_free_irq_vectors() on cleanup."
> 
> If it's not a bug, one could keep the docu that way or at least phrase
> it in a way so that no additional users start relying on that hybrid
> mechanism.

Thanks for the clarification, would you mind me sending a patch to fix
the description, and also mention the automatic clean-up behavior
shouldn't be relied anymore in new code?

...

> The good news is that it's the last remainder of PCI hybrid devres and
> getting rid of it would allow for removal of some additional code, too
> (e.g., is_enabled bit and pcim_pin_device()).
> 
> The bad news is that it's not super trivial to remove. I looked into it
> about two times and decided I can't invest that time currently. You
> need to go over all drivers again to see who uses pcim_enable_device(),
> then add free_irq_vecs() for them all and so on…

Do you think adding an implementation of pcim_alloc_irq_vectors(), that
always call pci_free_irq_vectors() regardless whether the PCI device is
managed, will help the conversion?

This will make it more trival to rewrite drivers depending on the
automatic clean-up behavior: since calling pci_free_irq_vectors()
several times is okay, we could simply change pci_alloc_irq_vectors() to
pcim_alloc_irq_vectors(), without considering where to call
pci_free_irq_vectors().

Introducing pcim_alloc_irq_vectors() will also help newly-introduced
drivers to reduce duplicated code to handle resource clean-up.

> If you give me a pointer I can provide a TODO entry. In any case, feel
> free to set me as a reviewer!

> Regards
> Philipp

Regards,
Yao Zi